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Histological variations in the walls of the digestive tract of salamanders

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Histological variations in the walls of the digestive tract of salamanders

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Content HISTÜLüGICiX VAHIATIUNS
lU THE
Y/ALLS UP THE DIGESTIVE TRACT
UP
SALAMAHDERS
A THESIS
P r e s e n t e d t o
th e P a c u l t y of th e D e p a rtm e n t o f Z oology
U n i v e r s i t y o f S o u th e r n C a l i f o r n i a
I n P a r t i a l P u l f i l l m e n t
o f th e R e q u ire m e n ts f o r t h e D eg ree
M a s te r o f S c ie n c e
by
Rena B a r n e t t
June 1940
UMI Number: EP67134
All rights reserved
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TABLE OF COBTEnTS
PAGE
I . imROBUGTION.............................................................................................. 1
I I . REVIEW OF LITERATURE......................................................................... 3
I I I . MATERIALS AND M ETHOD S....................................................................... 5
IV. ESOPHA GUS.................................................................................................. 16
1 . M ucosa 16
E p i t h e l i u m ............................................................................. 16
G l a n d s ....................................................................................... 2 0
M u s c u la r is m ucosae . . . . . . . . . . . . 22
2 . Subm ucosa . . . . . . . . . . . ......................... 23
P l i c a t i o n s . ................................................................... 23
3. M u s c u la r i s e x t e r n u s . ........................................................ 84
C i r c u l a r l a y e r ................................................................... 24
L o n g i t u d i n a l l a y e r ............................................................ 25
4 . S e r o s a ............................................................................................ 25
V. STOM ACH....................................................................................................... 26
1 . P o s i t i o n an d s i z e ........................................................ 26
2 . M ucosa o f sto m a c h . . . . . . . . . . . . . 26
E p it h e l i u m ............................................. 26
G l a n d s ....................................................................................... 27
F u n d ic .......................... . . . . . . . . . . . 28
P y l o r i c ............................................................................. 29
T u n ic a P r o p r i a . . . . . . . . . . . . . . 34
M u s c u la r is m ucosae ............................... . .. . . 36
3 . Subm ucosa . . . . . . . . . . . . . . . . . 38
P l i c a t i o n s ............................................................................. 38
4 . M u s c u la r i s e x t e r n u s ........................................................ 3 9
L o n g it u d i n a l l a y e r ........................................................ 4 0
C i r c u l a r l a y e r ................................................................... 4 0
5 . S e r o s a ............................................................................................ 42
6 . B lo o d and lym ph s y s t e m s ....................................... 42
V I. SMALL IHTESTIHE .................................................................. 43
1 . M ucosa o f i n t e s t i n e . . . . . . . . . . . . 4 3
E p i t h e l i u m ............................................................................. 4 3
C e l l t y p e s ........................................................................ 4 3
T u n ic a p r o p r i a ......................... 4 5
M u scu L aris m u c o s a e ................................... 4 5
11
Page
2 . S u b m u c o s a ......................................................... 47
G la n d s and ly m p h o id t i s s u e ..................... 47
P l i c a t i o n s .............................................................. 51
3 . D i v i s i o n s o f s m a ll i n t e s t i n e . . . . . 53
D u o d e n u m ......................... 54
Jeju n u m ..... ......................................... 54
Ileu m ........... .............................. . . . . . 54
4 . M uscle l a y e r o f th e i n t e s t i n e ..... 55
L o n g i t u d i n a l ......................................................... 55
C i r c u l a r ................................................................... 55
5. S e r o s a .............................................................................. 57
V I I . LAHGE I N T E S T IN E .............................................................................. 57
1. Mucosa o f l a r g e i n t e s t i n e . . . . . . . 57
E p i t h e l i u m .............................................................. 57
M u s c u la r is m ucosae . . . . 57
T u n ic a p r o p r i a .................................................... 57
2 . G la n d s ................... 57
3 . Subm ucosa ............................................ 57
P l i c a t i o n s ............................................. 57
4. M u s c u la r is E x t e r n i s .................................................. 57
C i r c u l a r l a y e r .................................................... 57
L o n g it u d i n a l l a y e r . 57
5. S e r o s a . . . . . . . . . . . . . . . . 57
V I I I . DISCUSSION ......................................................................................... 58
IX . SUMMARY .................................... 63
X. BIBLIOGRAPHY . .............................................................................. 70
I . INTRüDUCTIüH
The A nuran A m phibians have lo n g s e r v e d a s a v a l u a b l e
s o u r c e of m a t e r i a l f o r s c i e n t i f i c s t u d y . T h is i s due to
t h e i r a v a i l a b i l i t y , and t o th e f a c t t h a t some of t h e e a r l y
s t u d i e s o f t h e s e a n im a ls h a v e becom e c l a s s i c s o f r e s e a r c h .
N o tw ith s ta n d in g t h e l a r g e u s e of A nuran m a t e r i a l a c o m p le te
p i c t u r e o f th e A m phibian g ro u p i s n o t c o m p le te w ith o u t an
e q u a l amount o f s tu d y of t h e IT ro d eles w h ic h h av e b e e n
s l i g h t e d i n t h e m a t t e r of h i s t o l o g i c a l i n v e s t i g a t i o n .
S a la m a n d e rs a r e m ore p r i m i t i v e t h a n A nurans and a b e t t e r
know ledge of t h e i r m ic r o s c o p ic m orph o lo g y w i l l h e lp to
e x p l a i n v a r i a t i o n s w h ic h o c c u r i n h i g h e r v e r t e b r a t e s .
A s tu d y i s h e r e p r e s e n t e d i n w h ic h i s com pared
t h e h i s t o l o g i c a l d e t a i l s o f th e d i g e s t i v e t r a c t o f t h r e e
s a la m a n d e rs w h ich a r e knovm t o v a ry w id e ly i n h a b i t a t . W ith
t h i s p u r p o s e i n v ie w a cave fo rm , T yphlom olge r a t h b u n i -
S t e j n e g e r , an a r b o r e a l , A n e id es l u g u b r i s l u g u b r i s - H o l l o w e l l ,
and one w h ic h i n h a b i t s m o u n ta in s tr e a m s , T r i t u r o s t o r o s u s -
H a th k e , were e x am in e d . The s t r u c t u r e o f th e o rg a n s f o r th e
p r e h e n s i o n a n d r e t e n t i o n o f fo o d p r e v i o u s t o i t s p a s s a g e
i n t o th e e so p h a g u s h a s n o t b e e n t r e a t e d n o r h a s t h e c l o a c a .
The w r i t e r w is h e s to e x p r e s s h i s in d e b t e d n e s s t o
D r. B. M. H a r r is o n o f t h e Z oology D e p a rtm e n t, U n i v e r s i t y o f
S o u th e r n C a l i f o r n i a , u n d e r w hose s p o n s o r s h ip t h i s s y s t e m a t i c
s tu d y h a s b e e n u n d e r t a k e n and t o f r i e n d s who so k i n d ly
s u p p l i e d sp e c im e n s f o r r e s e a r c h .
I I . REVIEW OP LITERATURE
The h i s t o l o g y o f th e d i g e s t i v e t r a c t o f U r o d e le s h a s
r e c e i v e d o n ly c u r s o r y a t t e n t i o n o f a few i n v e s t i g a t o r s . I n
asm uch a s t h e l i t e r a t u r e c o n t a i n s l i t t l e t h a t p e r t a i n s
s p e c i f i c a l l y to s a la m a n d e r s , i t i s n e c e s s a r y , f o r t h e m ost
p a r t , t o r e v ie w t h a t l i t e r a t u r e w h ic h d e a l s w i t h c l o s e l y
r e l a t e d fo rm s l i k e th e f r o g and f i ^ e s a b o u t w hich much i s
known. Holm es (1935) and N oble (1931) h a v e w r i t t e n s t a n d a r d
b o o k s on th e b io lo g y o f th e A m p hib ian s b u t b o th c o n t a i n
l i t t l e a b o u t th e h i s t o l o g y o f th e d i g e s t i v e t r a c t o f U r o d e le s .
Ivlany i n v e s t i g a t o r s have s t u d i e d s e v e r a l e n d o c r i n a l g la n d s
and r e c e n t l y D a n ie l a n d Yarwood (193 9) h av e c o m p le te d r e
s e a r c h on t h e E a r l y E m bryology o f T r i t u r o s t o r o s u s . B lak e
(1 9 3 0 ) p u b l i s h e d on th e d i g e s t i v e t r a c t o f c e r t a i n T e l e o s t
f i s h e s and R o g ic k (1931) p u b l i s h e d on th e same t o p i c .
S u r r a r e r (1931) p u b l i s h e d a p a p e r on f i s h e s a l s o . W hile
t h e s e a r t i c l e s were n o t a b o u t s a la m a n d e r s , th e y s e r v e d a s a
s o u r c e o f v a l u a b l e m a t e r i a l f o r c o m p a ris o n . U ro d e l t i s s u e s
a r e n o t so h i g h ly s p e c i a l i z e d a s th o s e of h i g h e r v e r t e b r a t e s
y e t s t a n d a r d b o o k s a s th o s e by Cowdry (19E6) on c y to lo g y and
Maximow (1 9 3 0 ) on h i s t o l o g y a r e v a lu a b le a s g u id e s i n r e s e a r c h
p e r t a i n i n g to t h e s e s u b j e c t s .
P ig . 1 Typhlomolge rathbuni-
S ie jn e g e r .
B lin d cave s a la m a n d e r o f T ex a s.
N a t u r a l s i z e .
F I G il
I I I . - lÆATERIALS AND ÎCETHODS
Two s p e c i e s cf salam andLera u s e d i n t h i s t h e s i s
A n e id e s l u g u h r i s l u g u h r i s - H o H o w e ll and T r i t u r o s t o r o s u s -
R a th k o , a r c common t o C a l i f o r n i a . A n e id e s i s known by many
common nam es: -
C a l i f o r n i a Land S a la m a n d e r
S a d - c o lo r e d A n o id es
S p o t t e d A u to d ax
M o u rn fu l S a la m a n d e r
S p e c k le d S a la m a n d e r
T h is s p e c i e s o c c u r s c h i e f l y i n th e u p p e r S o n o ra n
L if e Zone th o u g h e x te n d in g i n t o t h e a d j a c e n t T r a n s i t i o n and
i n t o t h e Lower S o n o ra n . I t o c c u r s n o r t h a s f a r a s M endocino
C ounty and a s f a r s o u t h a s San D iego C ounty. T h is s a l a
m ander l i v e s i n h o llo w s o f oak t r e e s a n d a l s o on th e g ro u n d
b e n e a th s t o n e s and l o g s , a s a r u l e , i n oak w oods. S pecim ens
f o r t h i s t h e s i s came from B e r k e le y , C a l i f o r n i a .
The r a n g e of T r i t u r o s i s r e s t r i c t e d to P a c i f i c
d r a i n a g e a r e a s . I t o c c u r s i n th e U pp er S o n o ra n an d
T r a n s i t i o n L i f e Zones and i n h a b i t s th e v i c i n i t y o f s tr e a m s
an d p o n d s . F e m a le s l i v e u n d e r r o c k s and l o g s i n t h e f a l l
and w i n t e r , w h i l e t h e m a le s o f t e n re m a in i n t h e w a t e r . The
sp e c im e n s u s e d w e re o b t a i n e d i n W in te r C re e k , a b r a n c h o f
t h e B ig S a n ta A n i t a . The s k i n of th e fe n ia le i s ro u g h , and
d a r k e r th a n th e m ale i n th e a q u a t i c p e r i o d and i s a l s o p a p i l -
l a t e d . The m ales have a ro u g h e n e d a n d p a p i H a t e d s k i n d u r i n g
h i b e r n a t i o n , b u t a f t e r m o u lt and d u r in g a q u a t i c e x i s t e n c e , i t
becom es l i g h t i n c o l o r and sm o o th .
The w r i t e r was u n a b le to f i n d th e s p e c i e s T yphlom olge
r a t h b u n i - S t e j n e g e r , ( F ig . 1 ) , d e s c r i b e d i n any c h e c k l i s t o f
N o rth A m erican A m p h ib ia. I t i s one of tw> b l i n d A m phibia
fo u n d on t h i s c o n t i n e n t and h a s b e en s e e n i n i t s n a t i v e h a u n ts
by few s c i e n t i s t s a l t h o u g h i t s e x i s t e n c e h a s b e e n known s i n c e
1895 when fo u n d i n E z e l l ' s Gave n e a r San L larcos, T e x a s. The
e n t r a n c e t o t h i s cav e i s s m a ll an d l o c a t e d on th e s i d e o f a
h i l l . One h a s to make a p r e c a r i o u s t r i p i n t o t h e c a v e by
c lim b in g a ro u n d p r o j e c t i n g ro c k s and d e s c e n d in g p r e c i p i t o u s
s l o p e s ? d .th th e h e lp o f a s t e e l c a b le t o r e a c h th e p o o l w here
t h e a n im a ls l i v e . The w a te r a p p e a rs to be c o v e re d w i t h a
p r e c i p i t a t e b u t i s c l e a r and d eep w ith a n a rro w s h a llo w s h e l f
a ro u n d th e edge w here one may wade i n a ë i o r t d i s t a n c e . In
t h i s s t r a n g e e n v ir o n m e n t, t h e s e s a la m a n d e r s l i v e an d d ie
p r o b a b ly w ith o u t e v e r s e e i n g l i g h t . C o m p a ra tiv e ly few p l a c e s
on e a r t h hav e l e s s v a r y i n g te m p e r a tu r e v h io h i s s a i d t o be
a b o u t 6 0 °F .
T yphlom olg e i s a b e a u t i f u l , e x o t i c a n im a l w ith a
s i l k y w h ite body a n d t u f t e d g i l l s . The s k i n c o n t a i n s l i t t l e
p ig m e n t and th e body w a l l i s æ m i- t r a n s p a r e n t t o t h e e x t e n t
t h a t one may f a i n t l y s e e t h e i n t e r n a l o r g a n s . Mohr (1939)
c a p t u r e d a l i v e sp e cim en and s t a t e d t h a t th e g i l l s a r e b lo o d
r e d i n t h e l i v e sp e c im e n . The c r e a t u r e h a s s p i n d l y l e g s an d
an a n g u la r h e a d , t h e l a t t e r a p p e a r in g r e l a t i v e l y l a r g e i n
p r o p o r t i o n t o t h e r e s t o f th e b o d y , w h ic h i s no l a r g e r a ro u n d
t h a n a l e a d p e n c i l an d a p p r o x im a te ly f o u r in c h e s lo n g . T h is
s a la m a n d e r i s cons id e r e d a d e g e n e r a t e ty p e r e t a i n i n g i t s
l a r v a l fo rm p e rm a n e n tly a lth o u g h i t h a s th e pow er to re p ro d u c e .
I t p o s s e s s e s r u d im e n ta r y e y e s w h ic h , a c c o r d i n g t o N oble (1 9 3 5 ),
s t a r t t o d e v e lo p n o r m a lly and t h e n f o r some unknown r e a s o n
a r e a r r e s t e d , th e l i d s n e v e r s e p a r a t i n g , h e n c e th e a n im a l i s
s i g h t l e s s . The g e n u s , T yphlom olge r a t h b u n i , i s r e p r e s e n t e d by
t h e s i n g l e s p e c i e s . N oble s t a t e s t h a t t h i s s a la m a n d e r was
p o s s i b l y d e r i v e d from T y p h l o t r i t o n , f o r i t c l o s e l y a g r e e s w i t h
th e l a r v a o f E u ry c e a and o t h e r p r i m i t i v e P l e t h o d o n t i d s . The
sp e c im e n w orked on was o b t a i n e d fro m a B i o l o g i c a l S u p p ly
House a t D a l l a s , T e x a s.
To g a i n i n f o r m a t i o n r e s p e c t i n g th e f i n e r s t r u c t u r e o f
t h e t i s s u e s o f th e d i g e s t i v e t r a c t o f t h e s a la m a n d e rs i t i s
n e c e s s a r y to make p e rm a n e n t m ic r o s c o p ic s l i d e s . The s t e p s i n
t h e p r o d u c t i o n o f t h e s e s l i d e s a r e g ro u p e d u n d e r t h e f o llo w in g
8
h e a d s : (1 ) k i l l i n g and f i x i n g ; (E) d e h y d r a t in g ; (3 ) c le a r i n g ;
( 4 ) i n f i l t r a t i o n ; (5) im b e d d in g ; ( 6 ) s e c t i o n i n g ; (7) m o u n tin g
on s l i d e s ; ( 8 ) d i s s o l v i n g o f f the p a r a f f i n ; (9) s t a i n i n g .
To a v o id h a rm in g t h e t i s s u e s d e a t h s h o u ld come
q u i c k l y . The a n im a ls w ere p u t i n a t i g h t r e c e p t a c l e i n w hich
a p i e c e o f c o t t o n s a t u r a t e d w i t h c h lo r o f o r m was p l a c e d , and
a t i g h t c o v e r was p u t on i t .
The a n im a ls w ere ta k e n a s so o n a s p o s s i b l e a f t e r
d e a t h and b e f o r e p o s t m ortem c h an g e s o c c u r r e d . A lo n g
l o n g i t u d i n a l i n c i s i o n was made i n t h e v e n t r a l w a l l to e x p o se
th e i n t e r n a l o rg an s and t h e two s i d e s s p r e a d a p a r t . The
coelom was w ash ed o u t th o r o u g h ly w i t h i s o t o n i c s a l i n e
s o l u t i o n ( 0 .7 o f 1%), an d th e a n im a l was put i n t o a j a r c o n
t a i n i n g B o u in * s s o l u t i o n . T h is s o l u t i o n p e n e t r a t e d q u i c k l y ,
g a v e a d e l i c a t e f i x a t i o n , and t i s s u e s c o u ld b e l e f t i n i t
f o r a lo n g tim e w i t h o u t harm . I t p e n e t r a t e d a l l th e t i s s u e s
e q u a l l y w e l l , p u t ihe t i s s u e s i n a c o n d i t i o n to t a k e s t a i n s ,
h a rd e n e d th em so t h a t th e y would n o t be e a s i l y a l t e r e d by
t h e v a r i o u s s u c c e e d in g s t e p s , and b ro u g h t them t o t h e p r o p e r
c o n s i s t e n c y f o r c u t t i n g . A f t e r the a n im a l h ad s t a y e d i n
B o u in * s tw e lv e h o u rs o r l o n g e r , i t was r e a d y t o be t a k e n o u t ,
p in n e d down s e c u r e l y , and made re a d y f o r d i s s e c t i o n . The
t i s s u e s w e re k e p t m o is t w i t h B o u in * s w h ile th e o rg a n s w ere
b e in g rem o v e d . The d i g e s t i v e t r a c t was o b t a i n e d i n one
p i e c e and o u t i n t o s e c t i o n s a b o u t 1 cm. lo n g . E ach p ie c e
was p u t i n t o a s m a ll c h e e s e c l o t h b ag on th e end of w hich was
a t t a c h e d a l a b e l i n o r d e r to i d e n t i f y t h e t i s s u e s a c c u r a t e l y
and t o f a c i l i t a t e c h an g in g th e t i s s u e s fro m one r e a g e n t t o
a n o t h e r .
From B o u in * s th e t i s s u e s w e n t t o 70% a l c o h o l to
s t a r t th e d e h y d r a tin g p r o c e s s . B e g in n in g w i t h 70% a l c o h o l ,
t h e t i s s u e s w ere s u c c e s s i v e l y p u t th ro u g h 80%, 90%, 95% and
a b s o l u t e a l c o h o l . T is s u e s were l e f t i n th e 70% o r 80%
a l c o h o l i n d e f i n i t e l y w ith o u t h arm , b u t t h e y w ere n o t l e f t i n
th e h i g h e r p e r c e n t a l c o h o ls l o n g e r th a n one h o u r e a c h f o r
d a n g e r of th e t i s s u e s becom ing to o h a r d .
X y lo l c l e a r e d , r e p l a c e d t h e a l c o h o l an d f a c i l i t a t e d
th e p e n e t r a t i o n o f th e f i n a l m ounting medium. From th e
a b s o l u t e a l c o h o l , th e t i s s u e s w ere t r a n s f e r r e d t o a s o l u t i o n
o f 1 / 2 a b s o l u t e a l c o h o l and l / 2 x y l o l f o r an h o u r and t h e n
p u t i n t o p u re x y l o l f o r v a r i e d p e r i o d s fro m one t o t h r e e
h o u r s d e p en d in g upon t h e s i z e o f t h e t i s s u e .
I n f i l t r a t i o n , a g r a d u a l p r o c e s s , p r e p a r e d t h e t i s s u e s
f o r s e c t i o n i n g . H ence t h e y w ere p ut i n m e lte d p a r a f f i n f o r
a b o u t t h r e e h o u rs or l o n g e r . T his p r o v id e d a medium w h ic h
h e l d a n d s u p p o r te d th e m ost f r a g i l e t i s s u e s . The p a r a f f i n
10
was k e p t a t th e m e l t i n g p o i n t , u s u a l l y a ro u n d 5 2 ° o r 54^ C.
i n an o v e n . A g a l l o n l a r d c an ro u n d w hich had b e e n w rap p ed
a p i e c e o f w o o len m a t e r i a l two o r t h r e e tim e s made a good
o v e n . An e l e c t r i c d e s k lam p w hose r e f l e c t o r c o u ld b e b e n t
t o c o v e r t h e to p o f th e c a n f u r n i s h e d enough h e a t w h ich was
r e g u l a t e d by r a i s i n g o r lo w e rin g th e r e f l e c t o r above t h e c a n .
Im bedding p l a c e d th e t i s s u e s i n a medium t h a t c o u ld
be m ounted on v/ooden p lu g s an d o ut i n t h i n s e c t i o n s by th e
m ic ro to m e . H a rd e r p a r a f f i n t h a n t h a t p r e v i o u s l y m e n tio n e d
was r e q u i r e d when t h i n s e c t i o n s w ere d e s i r e d , and b a y b e r r y
wax a d d ed t o i t te n d e d t o lo w e r th e m e l t in g p o i n t w h ile
m aking i t h a r d e r and p r e v e n t in g c r y s t a l i z a t i o n . The p r o
p o r t i o n of b a y b e r r y wax t o p a r a f f i n was one p a r t b a y b e r r y
wax t o t e n p a r t s p a r a f f i n .
The em bedding p a r a f f i n was m e lte d when t h e t i s s u e s
w ere r e a d y t o come o ut o f t h e o v en . The p a r a f f i n was
m a in ta in e d i n t h i s s t a t e by s e t t i n g t h e b e a k e r c o n t a i n i n g
i t i n a p a n o f w a te r w hich h ad b e e n warmed b elo w th e
m e ltin g p o i n t (a b o u t 52° C . ) th e b e a k e r c o n t a i n i n g th e
t i s s u e w as s e t i n t h e same p a n . Enough s m a ll p a p e r b o x e s to
h o ld a l l t h e p i e c e s o f t i s s u e w ere r e a d y . The d im e n sio n s o f
t h e s e b o x es w ere 1" x 1” x 1 " . A bow l of c o ld w a te r was n e a r .
A f t e r p o u rin g a s m a ll am ount o f p a r a f f i n i n t o one o f th e p a p e r
b o x e s , a p i e c e o f t i s s u e was p l a c e d i n i t . T is s u e s w hich
11
w ere n o t w e l l o r i e n t e d w ere p r o p e r l y s p a c e d f o r c o n v e n ie n c e
o f c u t t i n g w i t h warm p i t h i n g n e e d l e s b e f o r e th e p a r a f f i n
h a rd e n e d . B o th tw e e z e r s and n e e d l e s w ere k e p t warm by
s ta n d in g them i n warm w a te r , b u t c a r e was t a k e n t o w ipe them
th o r o u g h ly d ry e a c h tim e b e f o r e t h e y w e re u s e d .
The p a r a f f i n was c o o le d q u i c k l y b y lo w e rin g th e
p a p e r box a lm o s t to i t s to p i n to a bowl of c o ld w a t e r . The
t o p s u r f a c e o f t h e p a r a f f i n was c o o le d by b lo w in g th e b r e a t h
on i t . When a t h i n f i l m had fo rm ed on th e t o p , a d ro p o r
tw o o f c o ld w a te r was a llo w e d t o flo w o v e r t h e t o p s u r f a c e .
A f t e r th e r e s i s t a n t f i l m of p a r a f f i n had s u f f i c i e n t l y
s o l i d i f i e d , t h e p a r a f f i n b o x was subm erged i n t h e w a te r .
The s i d e s of t h e box w ere p r e s s e d w i t h t h e f i n g e r s t o
p r e v e n t th e p a r a f f i n fro m fo rm in g a l i t t l e d e p r e s s i o n i n
t h e to p o f th e b l o c k . T h is k e p t the t i s s u e s c o v e re d and
made a b e t t e r sh a p e d b lo c k f o r m o u n tin g on th e wooden p l u g s .
The m a t e r i a l was l a b e l e d by w r i t i n g th e name o f th e t i s s u e
and num ber of t h e sp e cim en fro m w h ic h i t came on th e t a b s on
th e end o f the p a p e r b o x . The w h o le mass was p la c e d i n r u n
n in g w a te r f o r an h o u r or l o n g e r t o t h o r o u g h ly h a rd e n th e
p a r a f f i n . As so o n a s t h e b lo c k was c o o le d i t w as r e a d y f o r
s e c t i o n i n g o r t h e im bedded t i s s u e c o u ld be k e p t i n a c o o l
p l a c e i n d e f i n i t e l y .
12
To p r e p a r e t h e p a r a f f i n b l o c k s f o r s e c t i o n i n g , t h e y
w ere ta k e n o u t o f the p a p e r b o x e s a r û m ounted on wooden
p l u g s . The p lu g s w e re p l a c e d i n o o Id w a te r f o r f i v e o r t e n
m in u te s t o h a r d e n . The p a r a f f i n was th e n trim m ed w i t h a
s h a r p k n i f e t o make th e lo w e r and u p p e r e d g es p a r a l l e l . One
mm. o f p a r a f f i n was l e f t a ro u n d t h e t i s s u e . The b l o c k was
c a r e f u l l y a d j u s t e d i n t h e m ic ro to m e and th e i n d i c a t o r r e g u
l a t i n g t h e t h i c k n e s s o f th e s e c t i o n s was s e t a t s i x m ic ro n s
f o r s e c t i o n s f o r th e s tu d y o f c e l l s t r u c t u r e w ere b e s t c u t
a t t h a t t h i c k n e s s . When c o n d i t i o n s w ere r i g h t , th e s e c t i o n s
a d h e r e d t o one a n o t h e r , fo rm in g a r i b b o n a s t h e y w e re c u t by
t h e m ic ro to m e . As th e r i b b o n s w e re t a k e n fro m th e k n i f e ,
th e y w ere l a i d on a p i e c e o f p a p e r , l a b e l e d w i t h t h e name o f
th e t i s s u e an d i t s t h i c k n e s s . T h ese p a p e r s were p i l e d on
to p of one a n o th e r i n a s h a l l o w box and c o u ld be p r e s e r v e d
i n d e f i n i t e l y i n a c o o l p l a c e .
S e c ti o n s w e re m ounted on s l i d e s b e f o r e t h e y w ere
s t a i n e d . To a t t a c h t h e s e to t h e s l i d e s , a m ix tu r e o f w h ite
o f egg and g l y c e r i n e w as u s e d . A d ro p or more was p l a c e d
upon t h e s l i d e , and ru b b e d e v e n ly o v e r th e s u r f a c e u p o n
w hich t h e s e c t i o n s w ere p l a c e d . The f i l m was t h i c k enough
t o a ll o w th e f i n g e r t o g l i d e o v e r th e s u r f a c e e a s i l y . A few
d ro p s o f w a te r w ere p l a c e d upon t h e s l i d e w i t h a p i p e t t e
b e f o r e a s e c t i o n o f t h e p a r a f f i n r i b b o n of t h e d e s i r e d l e n g t h
was p ic k e d up w i t h a w et c a m e l^ s h a i r b r u s h and p l a c e d upon
13
i t s h in y a i d e down. To make s e r i a l s l i d e s , th e r ib b o n s w e re
p l a c e d i n row s one below t h e o t h e r k e e p in g them s t r a i g h t . A
p a n of h o t w a t e r was m a in ta in e d o v e r a B unsen b u r n e r a d
j u s t e d t o p r e v e n t b o i l i n g . A p i e c e o f window g l a s s was
p l a c e d on to p of th e p a n . The s l i d e s w e re p l a c e d on th e
g l a s s to s t r a i g h t e n o u t t h e w r i n k l e s i n t h e t i s s u e i f t h e r e
w ere a n y . The s l i d e s w e re t i l t e d s l i g h t l y t o a ll o w t h e
w a te r to d r a i n o f f and th e t i s s u e s t o s e t t l e on t h e f i x i t i v e .
I f s e c t i o n s w ere to o b a d ly w r i n k l e d , th e y w ere s t r a i g h t e n e d
by f l o a t i n g them on w a te r w hich was n o t h o t enough to m e lt
t h e p a r a f f i n . The s l i d e s w e re im m ersed w i t h th e f i x i t i v e
on them , i n t h e w a te r and s e c t i o n s w ere f l o a t e d o v e r th em
w i t h a b r u s h . The s l i d e s w e re t h e n draw n o u t o f th e w a te r
g e n t l y and th e t i s s u e s a d h e r e d t o them . E x c e ss w a te r was
d r a i n e d o f f and t h e s l i d e s w e re d r i e d a s much a s p o s s i b l e
w i t h f i l t e r p a p e r . The s l i d e s w ere p u t away to d r y i n th e
low t e m p e r a t u r e oven o r i n a s l i d e box f o r a few d a y s .
D i s s o lv i n g th e p a r a f f i n o f f the s l i d e s and s t a i n i n g
w ere th e f i n a l p r o c e s s e s . A s m a ll c o i l s p r i n g was u s e d to
h o ld e i g h t t o tw e lv e s l i d e s u p r i g h t i n th e r e a g e n t s and dyes
and to p r e v e n t t h e i r s u r f a c e s fro m t o u c h i n g . A lso i t e n a b
l e d t h e t e c h n i c i a n to t r a n s f e r t h e s l i d e s fro m one r e a g e n t
t o t h e n e x t i n one o p e r a t i o n . P e a n u t b u t t e r p i n t j a r s w ith
w ide m ouths and t i g h t c o v e r s h e ld th e r e a g e n t s and d y e s .
S e v e n te e n j a r s l a b e l e d a s f o llo w s s p e e d e d up p r o d u c t i o n o f
14
s l i d e s :
x y l o l
a b s o l u t e a l c o h o l
e o s i n
f o a l c o h o l
90% a l c o h o l
80% a l c o h o l
70% a l c o h o l
50% a l c o h o l
h a e m a to x y lin
A f t e r t h e t i s s u e s on t h e s l i d e s w ere dyed w i t h e o s i n
and h a e m a to x y lin and t h e p a r a f f i n was d i s s o l v e d fro m th em
c o v e r s l i p s w e re a d j u s t e d w i t h gum dam ar and t h e y w ere r e a d y
f o r s tu d y .
F i g . 2 A n e id e s l u g n b r i s l ii g u b r i a
W all, o f E so p h ag u s
C ro ss s e c t i o n X 355
GÜ - G o b le t c e l l
NÜ - N u c leu s
M M - M u s c u la ris m ucosa
LM - L o n g i t u d i n a l m u scle f i b e r s
SM - Submuoosa
CM - C i r c u l a r m uscle l a y e r
SLM - S t r i a t e d l o n g i t u d i n a l m uscle
f i b e r s
15
F IG . 2
16
IV. ESOPHAGUS
The e so p h a g u s p o s s e s s e s t h e f o u r t y p i c a l l a y e r s o f
a l l v e r t e b r a t e s . T h e re i s no s h a rp l i n e o f d e m a r c a tio n
s e p a r a t i n g t h e e so p h a g u s fro m th e p h a ry n x n o r fro m t h e
stom ach. The sto m ach i s i d e n t i f i e d by th e a b s e n c e of mucous
c e l l s i n i t s e p i t h e l i u m and by i t s g r e a t e r d i a m e t e r .
E p it h e l i u m - M ucosa. At t h e a n t e r i o r end o f th e
e so p h a g u s of A n e i d e s , th e m ucosa c o n s i s t s of a l a y e r of
p s e u d o s t r a t i f i e d m ucous c e l l s ( P ig . 2) o f t a l l co lu m n ar
ty p e b e in g e i g h t t o tw e lv e c e l l s w id e by a c t u a l c o u n t. The
o u t e r c e l l s a r e s l i g h t l y f l a t t e n e d on t h e i r d i s t a l f r e e en d s
w h ile t h e i r p r o x im a l e n d s , w h ic h r e s t upon c o n n e c t i v e t i s s u e
p a p i l l a e , a r e p o i n t e d . L i t t l e c y to p la s m i s p r e s e n t i n th e
p r o x im a l m d s of th e c e l l s i n w h ic h th e n u c l e i a r e l o c a t e d .
The b a s a l c e l l s o f t h e e p i t h e l i u m hav e s p h e r i c a l n u c l e i ;
t h o s e o f th e c e l l s n e x t to t h e lum en a r e e l o n g a t e ; w h i l e t h e
i n t e r m e d i a t e c e l l s p o s s e s s n u c l e i s l i g h t l y f l a t t e n e d . The
s i d e s o f t h e c e l l s b u lg e i n t y p i c a l mucous c e l l f a s h io n » a n d
th e p a r t c o n ta in i n g th e mucous s t a i n s l i g h t l y w ith h a e m a to x
y l i n and e o s i n w i t h a f i n e n e tw o rk o f p u r p l e r u n n in g th r o u g h
i t . T h is ty p e o f e p i t h e l i u m i s c o n s ta n t f o r a p p r o x im a te ly
t h r e e - f o u r t h s th e t o t a l l e n g t h o f t h e e s o p h a g u s , b u t as th e
sto m a c h i s a p p ro a c h e d , t h e c e l l s o f t h i s l a y e r g r a d u a l l y
c h an g e i n ty p e . Mucous c e l l s become l e s s num erous w h ile
17
t h e t a l l c o lu m n ar ty p e s i m i l a r t o th o s e v h ic h fo rm th e
l i n i n g of th e s to m a c h o f t h i s s a la m a n d e r becom e more num erous
u n t i l t h e y p r e d o m in a te . Ho c i l i a are o b s e rv e d on t h e c e l l s
l i n i n g th e lum en o f t h e e so p h ag u s o f A n e id e s .
The m ucosa o f T r i t u r o s i s s t r a t i f i e d c o lu m n a r, c o n
s i s t i n g of tw o k in d s o f c e l l s n a m e ly : ( l ) sim p le t a l l
c o lu m n a r; (2) g o b l e t c e l l s . A l l s im p le c o lu m n a r c e l l s h av e
c i l i a on t h e i r f r e e ends b u t t h e s e a r e l a c k i n g on th e g o b l e t
c e l l s . The c y to p la s m o f th e c o lu m n a r c e l l s i s d e n s e ly
g r a n u l a r n e x t t o th e lu m en . The f r e e b o r d e r of th e c e l l s
s t a i n s d a r k l y l i k e t h e s t r i a t i o n s fo u n d on t h e e p i t h e l i a l
c e l l s of th e i n t e s t i n e a n d th e c i l i a e x te n d beyond t h i s d a r k
l i n e .
The e s o p h a g e a l m u co sal e p i t h e l i u m o f T yphlom olge
( F i g . 3) i s m ore s im p le and p r i m i t i v e th a n t h e o t h e r two
s p e c i e s o b s e r v e d . T h is l a y e r i s fro m one t o t h r e e c e l l s
t h i c k . Two ty p e s of c e l l s a r e p r e s e n t a s i n T r i t u r o s f o r t h e
t o t a l l e n g t h o f th e o r g a n . A l l o f t h e s i m p le e p i t h e l i a l
c e l l s a r e c i l i a t e d , and a b o u t one i n t h r e e of a l l t h e c e l l s
i s m ucous. As t h e sto m ac h i s a p p ro a c h e d m ucous c e l l s become
l e s s num erous and f i n a l l y d i s a p p e a r . T h e re i s no a b r u p t
ch an g e from e s o p h a g e a l t o sto m a c h e p i t h e l i u m . The sto m a c h
e p i t h e l i u m r e t a i n s i t s c i l i a a f t e r i t h as l o s t i t s s t r a t i
f i e d a p p e a ra n c e and i s o b s e rv e d t o b e a s im p le l a y e r o n ly
F i g . 3 T yphlom olge r a t h b u n i
W all o f e so p h a g u s
C ro s s s e c t i o n X355
EP - E p it h e l i u m
G - G land o f e so p h a g u s
M M - M u s c u la r is m ucosa
SM - Sub m ucosa
CM - C i r c u l a r m u sc le l a y e r
LM - L o n g i t u d i n a l m u sc le l a y e r
S - S e r o s a
18
Fia.3
F i g . 4 A n eid ea lu g .u b ris l u ^ u b r i a
E so p h a g u s. C ro ss s e c t i o n . X102
G Ü - G o b le t c e l l
SM
-
Subm ucosa
EP - E p ith e H um
Ü
-
C h ie f c e l l
F - F undus of e s o p h a g e a l g la n d
PIT - P i t of e s o p h a g e a l g la n d
LM
- L o n g i t u d i n a l m u sc le l a y e r
S
-
S e r o s a
CM
-
C i r c u l a r m u sc le l a y e r
CA - C a p i l l a r y
G - E s o p h a g e a l g la n d
P
-
P a r i e t a l c e l l
F i g . 5 g r i t u r o a t o r o s u a
E s o p h a g e a l g la n d .
C ro s s s e c t i o n . X 355
P - P a r i e t a l c e l l
C - C h ie f c e l l
I» - Lumen o f g la n d
MJ - H ucl eus
19
PIT
FIG-.4
C
N U
F i d . 5
20
one c e l l i n t h i c k n e s s and v d th o u t g o b l e t c e l l s .
G la n d s . Eo e s o p h a g e a l g la n d s a r e o b s e r v e d a t th e
a n t e r i o r end of th e e so p h a g u s i n any o f th e t h r e e s p e c i e s .
I n A n e id e s an d T r i t u r e s , g l a n d s o c c u r i n t h e e s o p h a g e a l
m ucosa ( F ig . 4 ) w h ic h p e n e t r a t e th e subm ucosa a l s o . In t h e s e
two fo rm s t h e s e g la n d s a r e found i n o n ly a v e r y r e s t r i c t e d
r e g i o n n e a r th e sto m a c h , - i n A n e id es f o r a d i s t a n c e of
a b o u t one mm. and i n T r i t u r e s f o r a b o u t two mm. T hese g la n d s
a r e n o t num erous i n A n e id e s . Only o ne i s o b s e rv e d on some
c r o s s s e c t i o n s and n o t more th a n f o u r or f i v e on o t h e r s . In
A n e id e s th e y a r e l o c a t e d u s u a l l y on t h e d o r s a l o r l a t e r a l
s i d e s o f t h e e so p h a g u s w h ile i n T r i t u r e s th e y a r e m ore n e a r l y
c o n tin u o u s a ro u n d th e w a l l of t h e o r g a n . They g r a d u a l l y f a d e
o u t and e n t i r e l y d i s a p p e a r a s t h e s to m a c h i s a p p ro a c h e d .
N o b le (193 5) s t a t e s t h a t t h e s e e s o p h a g e a l g la n d s o c c u r j u s t
b e f o r e th e sto m ac h o f R ana and B ufo b u t do n o t o c c u r i n
v a r i o u s more p r i m i t i v e S a l i e n t i a o r i n c e r t a i n U r o d e le s .
The t u b u l e s o f t h e s e g la n d s e n t e r th e lum en of th e
e s o p h a g u s w h e re th e e p i t h e l i u m d i p s down b e tw e e n th e c o n n e c
t i v e t i s s u e p a p i l l a e . Some o f t h e l a r g e d u c ts a r e l i n e d w i t h
s t r a t i f i e d e p i t h e l i u m w h ic h r e s e m b le s t h e e p i t h e l i u m o f th e
f r e e s u r f a c e o f th e e so p h a g u s w h i l e o t h e r s a r e l i n e d w i t h
t a l l c o lu m n a r c e l l s w h ic h g r a d u a l l y become s h o r t co lu m n ar
a s t h e n e c k o f th e g la n d i s a p p ro a c h e d . I n some d u c ts c i l i a
21
a r e o b s e rv e d , w h ile o t h e r s e n l a r g e to form a o y s t - l i k e
d i l a t i o n , - a c o n d i t i o n found i n h ig h e r v e r t e b r a t e s . Two
t y p e s o f c e l l s a r e o b se rv e d i n t h e fun dus of th e g la n d s
( P ig . 5 ) : - ( l ) t h o s e t h a t s t a i n s l i g h t l y l i g h t e r and a r e
b e l i e v e d t o pro d u ce mucous; ( 2 ) t h o s e t h a t s t a i n d a r k e r and
re sem b le c h i e f c e l l s o f the g a s t r i c e p it h e l i u m o f t h e s e
s a la m a n d e rs . The f i r s t type has a n u c le u s i n th e b a s a l
p o r t i o n of the c e l l w hich s t a i n s d e e p p u r p l e . T h e ir c y t o
p lasm has a f i n e h a i r - l i k e n e tw o rk ru n n in g th r o u g h i t b u t
i s c l e a r e r th an t h a t of th e secon d t y p e . These c e l l s
re s e m b le p a r i e t a l c e l l s of th e g a s t r i c e p i t h e l i u m and a r e
p y ra m id a l i n sh a p e.
The second ty p e of c e l l o c c u rr in g i n th e fu n d u s o f
t h e s e g la n d s a r e s i m i l a r to c h i e f c e l l s of th e g a s t r i c g l a n d s .
They a r e p o ly g o n a l i n shape and a r e u s u a l l y l o c a t e d i n the
b a s a l p o r t i o n of t h e g la n d . They s t a i n d e e p ly w ith haema-
t o x o ly n . The c y to p la s m i s d e e p ly g r a n u l a r . The n u c l e i a r e
u s u a l l y s p h e r i c a l and l o c a t e d i n th e b a s a l p o r t i o n of th e
c e l l . These c e l l s a r e n o t so num erous a s t h o s e of th e o t h e r
t y p e , - o f t e n o nly one or two t o a c ro s s s e c t i o n o f a g la n d .
T hese g la n d s have a l a r g e lu m ai w ith s e v e r a l
b ra n c h e s fo rm in g a g r a p e - l i k e c l u s t e r w h ich e m p tie s i n t o one
t u b u l e . These g la n d s a r e not c o n tin u o u s a ro u n d t h e organ
b u t a p p e a r i n r e s t r i c t e d groups of from two t o f i v e . They
22
a l s o a r e in l i m i t e d a r e a s around the organ o f T r i t u r o s and
A n e id e s. F o r a d i s t a n c e of about two mm. j u s t a n t e r i o r to
th e stom ach t h e r e a r e none p r e s e n t i n t h e mucosa.
In T yphlom olge, e s o p h a g e a l g la n d s a r e d i s t r i b u t e d
i n t h e lo w e r h a l f o f t h e o rg a n . At f i r s t th e y a r e n o t
num erous, only one or two t o a c r o s s s e c t i o n . They g r a d u
a l l y i n c r e a s e in number u n t i l t h e y a r e fo u n d c o n tin u o u s ly
aro und th e e so p h a g u s. As t h e s e g la n d s become more n u m ero u s,
th e g o b l e t c e l l s d e c r e a s e i n number u n t i l th e y f i n a l l y d i s
a p p e a r fro m th e e p it h e l i u m . The fundus and n e c k of eac h
g la n d g r a d u a l l y become l o n g e r a s th e stom ach i s a p p ro a c h e d ,
and t h e r e is no a p p a re n t d i f f e r e n c e in c e l l s t r u c t u r e b e
tw een th e e s o p h a g e a l g la n d s and t h e g la n d s o f the a n t e r i o r
end of t h e fu n d u s o f th e stom ach. Noble s t a t e s , "They a r e
p e p s i n s e c r e t i n g s t r u c t u r e s and may be c o n s i d e r e d m o d if ie d
stom ach g l a n d s . "
M u scular is M ucosa. At th e a n t e r i o r end o f t h e
esophagus of A neides no m u s c u la r is mucosa i s a p p a r e n t n o r
f o r a b o u t o n e - f o u r t h i t s t o t a l l e n g t h . The m u s c u la r is
mucosa b e g in s a s clumps of sm ooth l o n g i t u d i n a l f i b e r s i n
i s o l a t e d g ro u p s l o c a t e d i n a few of th e p l i c a t i o n s and
g r a d u a l l y becom es a w e l l d e v e lo p e d l a y e r c o n s i s t i n g o f b o th
c i r c u l a r and l o n g i t u d i n a l f i b e r s . In A neides i t becomes
t h i c k e r th a n t h e musc u l a r i s e x t e r n u s and i s h e re s i x t o
23
e i g h t c e l l s t h i c k . The l o n g i t u d i n a l l a y e r i s n e v e r c o n t i n u
ous aroun d th e o rg a n h u t a p p e a r s alw ays a s clum ps. T his wide
m uscle hand i s o b se rv e d fo r about t w o - t h i r d s th e t o t a l l e n g t h
o f t h e p o s t e r i o r p o r t i o n o f th e eso p h ag u s.
I n T r i t u r o s th e mus c u l a r i s mucosa i s t h i c k e r th a n
t h a t o f A n e id e s. In p l a c e s the c i r c u l a r l a y e r v a r i e s i n
t h i c k n e s s from n in e to s i x t e e n f i b e r s w h i l e t h e l o n g i t u d i n a l
l a y e r a p p e a rs i n s c a t t e r e d c lu n k s r a t h e r th a n b e in g
c o n tin u o u s a ro u n d t h e o rg a n .
In Typhlom olge no musc u l a r i s mucosa i s fo u n d . I f
p r e s e n t , i t may b e f u s e d w ith th e m u s c u la r is e x t e r n u s , o r i t
i s p o s s i b l e t h a t a few i s o l a t e d f i b e r s a r e p r e s e n t .
Subm ucosa. The subm ucosa o f each of th e t h r e e
form s is t h i c k and is throw n i n t o num erous, w ide, l o n g i t u d i
n a l f o l d s . T h is a p p a r e n t l y e n a b le s th e esophagus to become
re m a rk a b ly d i s t e n s i b l e . T his l a y e r is a p p ro x im a te ly tw ic e
as wide a s t h a t of th e stom ach o r i n t e s t i n e and i n t h e s e
sa la m a n d e rs numerous b lo o d v e s s e l s and lymph s p a c e s o c c u r i n
i t . The p l i c a t i o n s v a ry i n number. In A neides a s many as
f i f t e e n to e i g h t e e n a r e o b se rv ed w h ile i n th e more p r i m i t i v e
Typhlom olge a s many a s t e n a re fo und i n one c r o s s s e c t i o n .
Sometimes w ide s p a c e s o ccur betw een p l i c a t i o n s i n Typhlom olge.
T r i t u r o s has t a l l , and i n many i n s t a n c e s , b ra n c h e d l e a f - l i k e
24
p l i c a t i o n s . No f u s in g of t h e s e p l i c a t i o n s a r e o b se rv e d
s i m i l a r to th e c o n d it i o n s fou nd i n t h e stom ach and i n t e s t i n e .
Musc u l a r i s e x t e r n u s . A neides p o s s e s s e s a p ro m in e n t
m u s c u la r is e x t e r n u s . At th e a n t e r i o r end of t l m esophagus
t h i s c o n s i s t s of a c i r c u l a r l a y e r e ig h t to t e n c e l l s wide o f
‘s t r i a t e d f i b e r s w hich a p p e a r i n b u n d le s h e l d t o g e t h e r by a
lo o s e c o n n e c tiv e t i s s u e . At a p o in t a p p ro x im a te ly o n e - h a l f
t h e l e n g t h of th e esop hagus t h i s l a y e r l o s e s i t s s t r i a t i o n s
and o n ly sm ooth m uscle f i b e r s a r e o b se rv e d and th e l a y e r a l s o
becomes t h i n n e r . The c i r c u l a r l a y e r a v e ra g e s a b o u t f i v e c e l l s
i n w id th w h ile th e l o n g i t u d i n a l f i b e r s a r e o b se rv e d i n p l a c e s
to be o n ly two or t h r e e i n w id th w h i l e i n o t h e r s t e n to
tw e lv e c e l l s may be c o u n te d . In some p l a c e s t h e l o n g i t u d i
n a l l a y e r i s c o n tin u o u s i n th e d o r s a l w a ll b u t e n t i r e l y
l a c k i n g i n th e l a t e r a l and v e n t r a l . At the a n t e r i o r end th e
l o n g i t u d i n a l l a y e r i s fo u n d on ly i n r e s t r i c t e d a r e a s , b u t
as the p o s t e r i o r r e g i o n i s a p p ro ach ed t h e r e a re p l a c e s where
i t o c c u rs c o n tin u o u s ly a ro u n d t h e o rg a n . A p p a re n tly t h e r e
i s no g r e a t need f o r a w e l l d e v e lo p e d l o n g i t u d i n a l m uscle
l a y e r .
The m'uscle l a y e r o f T r i t u r o s f o l lo w s i n g e n e r a l th e
same p a t t e r n and c o n d itio n s as th o s e o b se rv e d i n A n e id e s.
The a n t e r i o r p o r t i o n c o n s i s t s o f s t r i a t e d f i b e r s w h i l e th e
p o s t e r i o r p o r t i o n c o n s i s t s o f sm ooth. The c i r c u l a r l a y e r i s
25
th e t h i c k e r and i n th e w id e s t p l a c e s s i x t e e n t o tw en ty f i b e r s
can be c o u n te d , w h ile a t t h e n a r r o w e s t p o i n t t h e r e a r e o nly
s i x t o s e v e n f i b e r s .
In Typhlom olge t h e e x t e r n a l m uscle l a y e r i s n arrow
and no s t r i a t e d f i b e r s a r e o b se rv ed f o r t h e t o t a l l e n g t h o f
th e e so p h a g u s. Smooth i n v o l u n t a r y m uscle f i b e r s v a r y i n g i n
w id th from tv/o f i b e r s a t i t s n a rr o w e s t to f i v e t o s i x a t i t s
w i d e s t p o i n t . L ik e t h e o t h e r two specim en s no l o n g i t u d i n a l
l a y e r i s o b se rv e d a t th e a n t e r i o r end. T his l a y e r is sim p le
and c o n s i s t s u s u a l l y of i s o l a t e d clum ps. Not more th a n f i v e
o f th e s e clumps may be c o u n te d on any one c r o s s s e c t i o n .
Hence i t i s r e a s o n a b le to c o n c lu d e t h a t due to t h e t h i n n e s s
o f the m u s c u la r is e x t e r n u s , t h i s sa la m a n d e r must have to
depend l a r g e l y upon th e c i l i a as w e ll as p e r i s t a l t i c a c t i o n
o f th e m u sc le s to c a r r y i t s fo o d a lo n g the e so p h a g u s t o the
sto m ach .
S e ro s a . The s e r o s a o f th e lo w e r p o r t i o n o f t h e
eso p h ag u s i s a t h i n o u t e r c o a t composed of g r e a t l y f l a t t e n e d ,
e lo n g a te d c e l l s whose n u c l e i b u lg e i n t o t h e coelom .
26
V. STOMACH
P o s i t i o n and s i z e . The stom ach of a Salam ander
l i e s m ain ly i n t h e l e f t s i d e of th e body, and t u r n s s l i g h t l y
t o t h e l i g h t w ith i t s convex s i d e to w ard t h e l e f t . T here i s
no s h a r p c o n s t r i c t i o n s e p a r a t i n g th e esophagus from t h e
sto m ac h , b u t t h e a n t e r i o r end i s much w id e r t h a n the e so
phagus w here i t j o i n s t h e sto m ac h . At th e p y l o r i c end, th e
stom ach i s s e p a r a t e d fro m the i n t e s t i n e by a s h a r p c o n s t r i c
t i o n , and i s su s p e n d e d d o r s a l l y i n t h e coelom by th e d o r s a l
m esen tary , and v e n t r a l l y by t h e v e n t r a l m e s e n ta ry .
The w a ll of the sto m ach p o s s e s s e s f o u r c o a ts
t y p i c a l o f a l l v e r t e b r a t e s , (m ucosa, subm ucosa, m u s c u l a r i s ,
and s e r o s a . )
Mucosa o f t h e stom ach - E p i t h e l i u m . The in n e rm o st
c o a t , th e mucous membrane or t u n i c a m ucosa, is a t h i c k l a y e r
composed of g la n d s i n a s u p p o r t i n g m a t r ix of c o n n e c tiv e
t i s s u e , t h e t u n i c a p r o p r i a . The 0 1 t i r e g a s t r i c e p i t h e l i u m
i s a s i n g l e l a y e r of t a l l colum nar c e l l s whose l a r g e and
s p h e r i c a l o r s l i g h t l y f l a t t e n e d n u c l e i a r e u s u a l l y in t h e
b a s a l p o r t i o n of th e c e l l s b u t may o ccu r i n t h e m id d le . I t
i s b e l i e v e d t h a t t h e n u c l e i a r e found i n t h a t p o r t i o n o f th e
c e l l w here the g r e a t e s t a c t i v i t y o c c u r s . The c y to p la s m n e a r
t h e b a se of th e c e l l is f i n e l y g r a n u l a r and s t a i n s l i g h t e r
27
t h a n t h a t w h ich is n e x t to th e lumen w here i t i s c o a r s e l y
g r a n u l a r . In A neides l u g u b r i s l u g u b r i s and T r i t u r o s t o r o s u s
th e f r e e ends of t h e s e m ucosal c e l l s have b l u n t e n d s, b u t in
th e T. r a t h b u n i t h e b a s a l p o r t i o n o f each c e l l i s drawn o u t
i n t o lo n g p r o c e s s e s s i m i l a r to the c o n d i t i o n found i n th e
f r o g , w h ile t h e ends of the s to im c h ^ s m ucosal c e l l s f r e
q u e n tly have s h o r t p r o to p la s m ic p r o c e s s e s p r o j e c t i n g i n t o
t h e lum en. T his m ucosal e p i t h e l i u m r e s t s upon a basem ent
membrane t y p i c a l f o r m ost v e r t e b r a t e s .
G la n d s . The g a s t r i c g la n d s a re composed o f two
p a r t s ; - t h e o u t e r w hich i s th e g a s t r i c p i t , term ed th e
f o v e o l a g a s t r i c a , an d an i n n e r s e c r e t i n g p o r t i o n . The
s e c r e t i n g g la n d s v a r y fro m sim p le to com plex w ith th e s p e c i e s
and a l s o w ith the p o r t i o n of th e sto m ach from v^hich th e y come.
I f s im p le , (P ig . 6 ) o n ly one s l e n d e r c y l i n d r i c a l tu b u le j o i n s
th e p i t a t i t s b a se w h ile i n th e complex g la n d s t h e r e may be
as many as s i x or more t u b u l e s e n te r in g a s i n g l e p i t . In th e
f u n d ic p o r t i o n o f th e stom ach t h e s e b r a n c h in g g la n d s a r e n o t
so num erous as i n t h e p y l o r i c r e g i o n . Of th e t h r e e amphib
ia n s s t u d i e d the l i t t l e b l i n d sa la m a n d e r u n d o u b te d ly h a s th e
most sim p le g la n d s t r u c t u r e . In t h i s a n im a l most o f th e
g la n d s a r e s im p le i n th e f u n d ic p o r t i o n o f th e o rg a n , a l
th o u g h b o t h t y p e s of t u b u l e s a re f a i r l y common, w h ile i n t h e
p y l o r i c p o r t i o n t h r e e o r f o u r b ra n c h e s can be o b se rv e d . The
F i g .
6 . T yphlom olge r a t h h u n i .
G a s t r i c g la n d s of the fundus o f
stom ach. C ross s e c t i o n . X 355
EP - E p ith e liu m
GP
-
G a s t r i c P i t
N - Neck o f g lan d
G - G a s t r i c g l a n d
F
-
F undus o f g la n d
TP - T u n ic a p r o p r i a
M M
-
M a e c u la r is mucosa
SM
-
Suhmucosa
M C J Mucosa
28
w
FIG. 6
29
p r o p o r t i o n o f b ra n c h e d complex ty p e of g la n d i n th e fiindus to
th e s im p le ones i s a p p ro x im a te ly t h i r t y p e r c e n t c o u n tin g
c e l l s i n com parab le a r e a s w h ile i n the p y l o r i c r e g i o n about
s i x t y p e r c en t a r e of the complex ty p e . T. t o r o s u s h as th e
m ost complex g la n d s of t h e t h r e e sp e cim en s. In t h i s a n im a l,
b ra n c h in g t u b u l e s a p p e a r f r e q u e n t l y b o th i n th e c a r d i a c and
p y l o r i c r e g i o n . M oreover i n th e p y l o r i c r e g i o n th e t u b u l e s
b ra n c h a t t h e i r d i s t a l e n d s , - a c o n d i t i o n a p p a r e n t l y n o t
o c c u r r in g i n e i t h e r of the o t h e r two s p e c i e s . In a l l t h r e e
s p e c i e s the d i s t a l ends of the t u b u l e s end b l i n d l y i n s l i g h t l y
b u lb o u s e n la r g e m e n ts .
The g a s t r i c p i t s i n each a n im a l u n d e r c o n s i d e r a t i o n
a r e l i n e d w ith e p i t h e l i u m # i i c h a p p e a rs to be an i n v a g i n a t i o n
o f t h a t which i s found on th e f r e e s u r f a c e of t h e lum en. In
t h e T r i t u r o s and A n e id e s , th e c e l l s a r e of th e t a l l colum nar
ty p e w ith l a r g e n u c l e i , s p h e r i c a l or s l i g h t l y e l o n g a t e ,
l o c a t e d i n the b a s a l p o r t i o n of th e c e l l s (F ig . 7 ). How
e v e r , i n th e T yphlom olge, c u b e i d a l c e l l s a r e a l s o o b se rv e d
l i n i n g th e g a s t r i c p i t s and Vvhere colum nar c e l l s o c c u r, a r e
o b s e rv e d to be r e l a t i v e l y s h o r t e r t h a n th o s e i n th e o t h e r two
s p e c i e s . In the t h r e e specim ens s t u d i e d , th e c y to p la sm
a d j a c e n t to th e p i t s lumen i s more d e n s e ly g r a n u l a r t h a n t h a t
w hich is f u r t h e r fro m i t . A lso i t is o b se rv e d i n e a c h of t h e
P i g . 7. T r i t u r o a t o r o s u s
G a a t r i c g la n d s of th e p y l o r i c stom ach
C ro ss s e c t i o n . X 355
GP - G a s t r i c p i t
IT - Keck o f g la n d
G - G a s t r i c gland
P - P a r i e t a l c e l l
P - Fundus of g la n d
M M - M u s c u la ris mucosa
EP - E p ith e liu m
TP - T u n ica p r o p r i a
0 - C h ie f c e l l
CM - C i r c u l a r m u scle l a y e r
IM - L o n g i t u d i n a l m uscle l a y e r
30
FI0.7
F i g . 8. gyphlom olge r a t h t i m i
P y l o r i c stom ach g l a n d s . C ro ss s e c t i o n
% 355
GP - G a s t r i c p i t
EP - E p it h e l i u m
TP - T u n ic a p r o p r i a
E - Heck of g lan d
F - Fundus
6 - G a s t r i c gland
BM - Basement membrane
M M - M u s c u la r is mucosae
SM - Suhmucosa
F i g . 9. A neides l u g u h r i s l u g u h r i s
C a rd ia c stom ach g l a n d . C ross s e c t i o n
X 355
1 - lumen
0 - C h ie f c e l l
P - P a r i e t a l c e l l
31
EP
TP
BM
M M
SM
PIG. 8
P
F IG .9
32
t h r e e , t h a t i n p a s s i n g dowi th e p i t s the c e l l s become g r a d u
a l l y s h o r t e r . In Typhlom olge th e n u c l e i a r e l a r g e and
occupy th e g r e a t e r p a r t of t h e c e l l s (F ig . 8 . ) In A neides
t h e n u c l e i i n th e c e l l s a t th e neck of the g la n d a r e n e a r l y
alw ays s p h e r i c a l , w h ile i n t h e o th e r two more v a r i a t i o n
o c c u rs as the f l a t t e n e d fo rm s a r e common.
The t u b u l e s a r e l i n e d w ith two k in d s o f c e l l s , -
th e c h i e f and th e p a r i e t a l . Of t h e s e tw o, th e fo rm e r a re
th e more num erous, and on ly a s m a ll p o r t i o n o f e a c h r e a c h e s
t h e lum en of th e t u b u l e . The c y to p la s m i s d e e p ly g r a n u l a r
n e a r t h e lumen and th e n u c l e i , i n a lm o st e v ery c a s e , a r e
i n th e b a s a l p a r t of th e c e l l . W hile c h i e f c e l l s a r e fou nd
th r o u g h o u t th e e n t i r e l e n g t h o f t h e g a s t r i c t u b u l e s th e y a r e
m ost numerous a t t h e i r d i s t a l en ds. They s t a i n d a r k l y and
a r e p y ra m id a l or p o ly g o n a l i n s h a p e , - t h e l a t t e r b e in g t h e
more common. T hese c h i e f c e l l s a r e th o u g h t i n t h e human to
s e c r e t e t h e p e p s i n o f the g a s t r i c j u i c e . T h is ty p e form s
a lm o st th e e n t i r e l e n g t h o f t h e t u b u l e s of th e p y l o r i c
p o r t i o n . Where p a r i e t a l c e l l s o c cu r i n t h i s r e g i o n t h e y a r e
fo u n d l o c a t e d j u s t b e lo w the n e c k o f th e g la n d o r i n f r e q u
ently a c e l l i s i s o l a t e d somewhere i n th e u p p e r t h i r d o f th e
t u b u l e s .
J u s t b e lo w th e n eck of th e ^ a n d , c e l l s whose
c y to p la s m s t a i n v e ry l i g h t l y , a r e u s u a l l y fo u n d . These a r e
32
th e p a r i e t a l c e l l s w hich in the human a re known to s e c r e t e
h y d r o c l o r i c a c i d . They a r e som etim es crowded away from th e
lumen of the t u b u l e . These c e l l s t a k e a l i g h t e r s t a i n th a n
th e c h i e f c e l l s p ro b a b ly b ecause t h e i r chem ical c o n te n t i s
d i f f e r e n t . They a re o b serv ed t o be l e s s g r a n u l a r th a n th e
c h i e f c e l l s a l s o . T h e ir c y to p la sm i s c l e a r e r and t h e i r
g r a n u le s a re f i n e r , w h ile t h e i r s p h e r i c a l n u c l e i a re s m a lle r
th a n th o se of th e c h i e f c e l l s a lth o u g h the c e l l s , th e m se lv e s,
a re l a r g e r i n s i z e (F ig . 9 ).
In each o f t h e t h r e e an im als s t u d i e d , p a r i e t a l c e l l s
a r e most numerous i n the fu n d ic p o r t i o n o f th e stom ach. In
T. t o r o s u s as much as o n e - h a l f t o t h r e e - f o u r t h s o f th e e n t i r e
l e n g t h of t h e tu b u le s a re composed o f p a r i e t a l c e l l s w h ile
c h i e f c e l l s a re c o n fin e d i n t h e extreme b l i n d ends. In
T. r a t h b u n i p a r i e t a l c e l l s a r e found alm o st the e n t i r e
l e n g t h o f th e f u n d i c t u b u le s and only a few c h i e f c e l l s
occur a t th e extreioe d i s t a l end. In some tu b u le s o n ly fo u r
or f i v e of the l a t t e r type can be c o u n te d . This c o n d itio n
i s found i n t h e ^ l u g u b r i s l u g u b r i s a l s o , b u t c h i e f c e l l s
a r e o b serv ed to be i n t e r s p e r s e d f r e q u e n t l y among them.
The g l a r d s of t h e fundus a re r e a d i l y d i s t i n g u i s h e d
from th o se of the p y l o r i c p o r t i o n , by t h e l e n g t h of the
t u b u l e s , th e s t a i n i n g o f t h e c e l l s , an d th e s i z e of t h e
lumen. In th e c a r d i a c r e g i o n th e tu b u le s a r e lo n g e r and
F i g . 10. T r i t u r o s t o r o s u s .
P y l o r i c stom ach show ing
d e t a i l e d s t r u c t u r e of mucosa and
suhm ucosa. C ross S e c t i o n . X102
EP E p it h e l i u m
G — G a s t r i c g la n d s
TP T u n ic a p r o p r i a
CM C i r c u l a r m uscle l a y e r
IM — L o n g it u d i n a l m u scle l a y e r
SM Suhmuc o sa
35
FIG *10
36
t h e t i m i c a p r o p r i a a l s o form s th e c o n n e c tiv e t i s s u e c o re s of
th e v i l l i . The c e l l s o f t h i s c o n n e c t i v e t i s s u e a r e e lo n g a te
and have s m a ll f l a t t e n e d o r s t e l l a t e n u c l e i , and c a p i l l a r i e s
a r e num erous.
M u s c u la ris m u co sae. The m u s c u la r is mucosae c o n s i s t s
o f two l a y e r s , th e i n n e r c i r c u l a r and th e o u t e r l o n g i t u d i n a l .
T h is l a y e r v a r i e s i n t h i c l m e s s i n t h e t h r e e s p e c i e s and i n
e ac h c a s e i s r e l a t i v e l y t h i c k e r i n c e r t a i n a r e a s t h a n i n
o t h e r s . In A neidea t h i s l a y e r i s t h i c k e s t w here th e l a r g e
p l i c a e a r e l o c a t e d .
The p l i c a e a r e form ed hy th e suhm ucosa w hich i s
th ro w n i n t o t h e l a r g e l a t e r a l f o l d s (F ig . 1 0 ) . The number of
t h e s e i s n o t c o n s t a n t and v a r i e s when s e e n i n c ro s s s e c t i o n
from t h r e e to s i x in number a s one goes fro m t h e a n t e r i o r to
t h e p o s t e r i o r e n d of th e sto m ac h . They emerge w i t h t h e i r
m ucosal c o v e rin g from th e l a t e r a l and d o r s a l w a l l s and p r o
t r u d e i n t o t h e lumen of th e sto m ac h , - t h e v e n t r a l and d o r s a l
w a l l s a r e i d e n t i f i e d by t h e a tta c h m e n ts of t h e s e m e s e n t a r i e s .
A lso i n ^ l u g u b r i s l u g u b r i s th e m u s c u la r is mucosae
c o n s i s t s a lm o st e n t i r e l y of c i r c u l a r f i b e r s v /h ile l o n g i t u d i
n a l f i b e r s o c c u r i n f r e q u e n t l y i n s m a ll g ro u p s s e p a r a t e d by
w ide s p a c e s w here none a r e fo u n d . The w id th o f any l a y e r
v a r i e s fro m a s i n g l e c e l l to e i g h t or t e n . In Typhlom olge
r a t h b u n i th e m uscle l a y e r of t h e mucosa i s t h i c k e r t h a n the
F i g . 11. Typhlom olge r a t h b u n i .
Fundus of th e sto m a c h . G ross s e c t i o n . X 102
G - G a s t r i c g la n d s
M M - M u s c u la r is mucosa
SM - Suhmucosa
CM - C i r c u l a r m uscle l a y e r
S - S e r o s a
IiM - L o n g i t u d i n a l m uscle l a y e r
EP - E p it h e l i u m
TP - T u n ic a p r o p r i a
GA - C a p i l l a r y
F i g . 12* T r i t u r o s t o r o s u s
W all o f p y l o r i c stom ach. G ro ss s e c t i o n . X 102
TP - T u n ic a p r o p r i a
M M
-
M u s c u la r is mucosa
CA - C a p i l l a r y
EP - E p it h e l i u m
G - G a s t r i c g lan d
SM
-
Suhmucosa
GM
-
C i r c u l a r m uscle l a y e r
LM - L o n g i t u d i n a l m u scle l a y e r
S
—
S e r o s a
37
F IG .11
Tf
S M
f i g . 12
38
t u n i c a m u a c u la r is i n th e fu n d io p o r t i o n and i s c o n tin u o u s
a ro u n d th e o rg a n ( P ig . 1 1 ) . The l o n g i t u d i n a l l a y e r i s
d e v e lo p e d b e t t e r t h a n i n e i t h e r of th e o t h e r two s p e c i e s
s t u d i e d and i n p o r t i o n s of t h e f u n d ic r e g i o n i t i s w id e r th a n
th e c i r c u l a r l a y e r . In t h e p y l o r i c p o r t i o n , th e m u s c u la r is
mucosae i s w id e r on t h e d o r s a l s i d e . In T r i t u r o s t o r o s u s
t h i s l a y e r i s w e ll d e v e lo p e d . C i r c u l a r f i b e r s a r e most i n
e v id e n c e and t h i s l a y e r is t h i c k e r i n some a r e a s w h i l e i t
t h i n s o u t i n o t h e r s . T h is is t r u e of the l o n g i t u d i n a l
l a y e r a l s o . In some p l a c e s th e m u s c u l a r i s mucosae c o v e rs
th e p l i c a e form ed by f o l d s o f t h e subm ucosa and b o th l a y e r s
a r e w e l l d e v e lo p e d , w h ile i n o t h e r p l a c e s t h e l o n g i t u d i n a l
l a y e r h a s in v a d e d t h e p l i c a e t o a p p e a r i n t h e i r d i s t a l
e x t r e m i t i e s as l a r g e clumps o f f i b e r s (P ig . 1 0 ) , a c o n d i t i o n
n o t fo u n d i n t h e o t h e r two s p e c i e s s t u d i e d . At the p o s t e r i o r
end of the stom ach t h e l a y e r i s much n a r r o w e r . T here a r e
o n ly a few l o n g i t u d i n a l f i b e r s a r r a n g e d i n clumps i n th e
p l i c a e w h ile t h e r e a r e w id e s p a c e s where t h e y do n o t o c cu r
and t h e c i r c u l a r m u sc le f i b e r s a r e n o t so numerous i n t h i s
r e g i o n ( P ig . 1 1 ).
Submucosa - P l i c a t i o n s . The subm ucosa a s u s u a l i s
composed m ain ly of c o n n e c tiv e t i s s u e c o n t a i n i n g numerous
b lo o d v e s s e l s and f a t c e l l s . G re a t v a r i a t i o n i n t h i s r e g a r d
o c c u rs among the t h r e e s p e c i e s . In A n e id es t h e subm ucosa i s
throv/n i n t o lo n g l a t e r a l p l i c a e , and i n th e p y l o r i c r e g i o n
39
t h e f r e e edges of th e p l i c a e f u s e w i t h one a n o th e r fo rm in g
se c o n d a ry lu m in a b u t n e v e r more th a n one of t h e s e i s
o b se rv e d i n one c ro s s s e c t i o n . U s u a lly t h i s f u s i n g ta k e s
p l a c e b etw een a d j a c e n t p l i c a e b u t som etim es t h o s e fro m
o p p o s i t e s i d e s f u s e . No p l i c a e o c c u r i n th e v e n t r a l w a l l of
t h e stom ach w h ere a l l t h e l a y e r s of t i s s u e a r e t h i n n e r i n
e ach of th e t h r e e s p e c i e s s t u d i e d .
P l i c a e a r e n o t o b se rv e d i n Typhlomolge r a t h b u n i , b u t
th e subm ucosa i s t h i c k e r on the d o r s a l s i d e of th e p y l o r i c
sto m ac h , - th e s i g n i f i c a n c e of vihich th e w r i t e r was u n a b le to
d e te r m in e . In T r i t u r o s t o r o s u s ( P ig . IE) th e subm ucosa form s
l a r g e p l i c a e which a r e l o c a t e d on the d o r s a l and l a t e r a l
s i d e s but th e y do n o t f u s e w ith one a n o t h e r . T h is v a r i a t i o n
may b e th e r e s u l t o f d i f f e r e n c e s i n fo o d h a b i t s .
Musc u l a r i s e x t e r n u s . An i n n e r c i r c u l a r and an o u t e r
l o n g i t u d i n a l l a y e r o f m uscle f i b e r s c o n s t i t u t e th e t u n i c a
musc u l a r i s . T his m u sc le l a y e r form s a t h i c k a r e a v h ic h
v a r i e s i n w id th i n d i f f e r e n t p o r t i o n s o f t h e same sto m a c h and
i n th e same r e g i o n s of t h e s e t h r e e s p e c i e s . I n each s p e c i e s
o b s e r v e d , th e m u scle l a y e r i s a lw ay s t h i c k e r i n t h e d o r s a l
w a l l th r o u g h o u t th e e n t i r e l e n g t h of t h e stom ach. A lso the
p y l o r i c p o r t i o n h a s t h e w i d e s t m uscle l a y e r . In th e fu n d u s
o f Typhlom olge th e e n t i r e m u sc le l a y e r is t h i n .
40
L o n g i t u d i n a l l a y e r . I n some p o r t i o n s the l o n g i
t u d i n a l l a y e r ( F ig . 13) e q u a ls the c i r c u l a r l a y e r i n t h i c k
n e s s and form s a c o n tin u o u s band a ro u n d the stom ach, - a
c o n d i t i o n a ls o o b se rv e d i n T r i t u r o s . In the a n t e r i o r r e g i o n s
o f th e f u n d u s , t h i s l a y e r i s n o t c o n ti n u o u s , b u t th e f i b e r s
o c c u r in clum ps s e p a r a t e d by c o n n e c tiv e t i s s u e . T his
c o n d i t i o n i s fo u n d i n a l l t h r e e s p e c i e s . In A n e id e s, th e
l o n g i t u d i n a l l a y e r i s t h i n th r o u g h o u t t h e e n t i r e l e n g t h of
th e sto m ach , clum ping of f i b e r s b e in g the u s u a l a rra n g e m e n t
i n the fu n d u s w i t h p l a c e s o c c u r r i n g i n w hich o n ly c o n n e c tiv e
t i s s u e is o b s e r v e d . In T r i t u r o s , the l o n g i t u d i n a l l a y e r
fo rm s a t h i n c o n tin u o u s band which v a r i e s i n v d d th from one-
f i f t h to f o u r - f i f t h s t h e w id th of the c i r c u l a r l a y e r .
C i r c u l a r l a y e r . The c i r c u l a r m u sc le f i b e r s form a
much t h i c k e r l a y e r th an t h e l o n g i t u d i n a l i n the p y l o r i c
r e g i o n o f a l l t h r e e s p e c i e s t h a n i n th e fu n d u s b o th i n th e
d o r s a l and l a t e r a l w a l l s . The c i r c u l a r l a y e r i n th e l a t e r a l
w a l l s of T r i t u r o s i s a p p r o x im a te ly o n e - t h i r d th e t h i c k n e s s of
i t i n the d o r s a l p o r t i o n and abo u t o n e - h a l f t h e t h i c k n e s s i n
t h e v e n t r a l p a r t . The same v a r i a t i o n o c c u rs i n b o t h
Typhlom olge and A n e id e s. The f a c t t h a t th e t u n i c a musc u l a r i s
as w e l l as th e mucosa i s w id e r i n the p y l o r i c r e g i o n th a n i n
th e fu n d u s i n d i c a t e s t h a t more d i g e s t i o n and a b s o r p t i o n t a k e s
p l a c e h e r e . In t h i s r e g i o n t h e l o n g i t u d i n a l l a y e r is a p p r o x i -
F i g . 13. Typhlom olge r a t h b u n i
P y l o r i c stom ach a rra n g e m e n t o f l a y e r s o f
t i s s u e . C ro ss s e c t i o n . X lOE
EP - E p it h e l i u m
G - G a s t r i c g la n d s
TP - T u n ic a p r o p r i a
CM - C i r c u l a r m uscle l a y e r
LM - L o n g it u d i n a l m u sc le l a y e r
MM - M u scu lar i s mucosae
CA - C a p i l l a r y
SM - Submucosa
S - S e r o s a
F i g . 14. A neides l u g u b r i s l u g u b r i s
D e t a i l s of e p it h e l i u m of th e duodenum.
C ross s e c t i o n . X 365
GO — G o b le t c e l l
EP E p it h e l i u m
STR S t r i a t i o n of colum nar c e l l
CA C a p i l l a r y
SM Submucosa
41
F IG .13
STR
FIG. 14
4E
m a te ly o n e - t w e n t i e t h t h e t h i o k n e s s o f t h e c i r c u l a r l a y e r i n
th e d o r s a l w a l l , w h ile on th e l a t e r a l s i d e s , where the
c i r c u l a r l a y e r i s n a r r o w e s t , i t i s a b o u t o n e - t e n t h t h e
t h i c k n e s s .
The m uscle c e l l s a r e commonly s p i n d l e sh a p ed w i t h a
s i n g l e n u c le u s n e a r t h e c e n t e r of th e c e l l . U s u a l l y the
n u c l e i a r e s p i n d l e s h a p e d , b u t s p h e r i c a l o r s l i g h t l y
f l a t t e n e d n u c l e i c a n b e o b se rv e d i n a l l t h r e e s p e c i e s
s t u d i e d . P o s s i b l y t h i s v a r i a t i o n o f n u c l e i may be due to
t h e p r i m i t i v e n a t u r e o f th e an im als u n d e r c o n s i d e r a t i o n
whose t i s s u e s a re n o t so h i g h l y d i f f e r e n t i a t e d a s t h o s e of
h i g h e r v e r t e b r a t e s .
S e r o s a . The s e r o s a o f th e stom ach i s a t h i n o u t e r
c o a t composed o f g r e a t l y f l a t t e n e d , e lo n g a te d c e l l s . T his
c o v e r in g i s c o n tin u o u s w ith t h e d o r s a l an d v e n t r a l m esen
t e r i e s where th e y j o i n t h e stom ach.
B loo d and Lymph s y s te m s . The stom achs o f a l l t h r e e
s p e c i e s a r e w e l l s u p p l i e d w i t h b lo o d v e s s e l s an d c o rre s p o n d
t o t h e c o n d i t i o n which i s n o rm al o f a l l v e r t e b r a t e s . I n
T yphlom olge and T r i t u r o s no lymph nod es a r e o b se rv e d i n th e
w a l l s of t h e stom ach, b u t i n A neides t h e y o c c u r i n f r e q u e n t l y
i n t h e t u n i c a m u sc u la r i s .
43
VI. Q IA A LL IIÎTESÏIIŒ
The s m a ll i n t e s t i n e i s c o n tin u o u s w ith the c a u d a l end
o f th e stom ach fo rm in g an a n g le w ith i t and s e p a r a t e d from
t h a t o rg a n by a c o n s t r i c t i o n , th e p y l o r u s . The duodenum i s
n e a r l y s t r a i g h t and p a r a l l e l t o t h e sto m ac h . There i s a
s h o r t jejunum and t h e ile u m form s th e r e m a in in g lo n g e r
p o r t i o n . The d ia m e te r i s n e a r l y u n ifo rm th ro u g h o u t i t s c o u rs e
b u t i s much l e s s t h a n th e sto m ach . The i n t e s t i n e i s f a s t e n e d
t o t h e m id - d o r s a l p o r t i o n of t h e body c a v i t y by th e m e s e n te ry .
A s m a ll v e n t r a l m e s e n te ry c o n n e c ts t h e i n t e s t i n e t o th e l i v e r .
Mucosa. In the i n t e s t i n a l mucosa two ty p e s of c e l l s
a r e a p p a r e n t , n am ely , g o b l e t and colum nar e p i t h e l i a l c e l l s .
In th e h i g h e r v e r t e b r a t e s g o b l e t c e l l s a r e known to s e c r e t e
m ucous. These c e l l s a r e num erous th r o u g h o u t t h e e n t i r e
l e n g t h of th e i n t e s t i n e s . The young g o b l e t c e l l s c o n t a i n
l a r g e g r a n u l e s i n t h e i r c y to p la sm known as m ucinogen
g r a n u l e s and Bremer s t a t e s t h a t i n man t h e s e a r e changed
i n t o mucous. At f i r s t th e mucous i s form ed i n t i n y d r o p l e t s
w h ich g r a d u a l l y i n c r e a s e i n s i z e and f u s e t o f i l l t h e f r e e
end of th e c e l l . As th e s e c r e t i o n f i l l s th e c e l l , th e
n u c le u s and c y to p la s m a r e crowded i n t o th e d i s t a l end. I n
young c e l l s where the mucous i s b e g in n in g t o form , i t i s
o b se rv e d to ta k e a b r i g h t deep r e d s t a i n w h ile i n o l d e r c e l l s
i t t a k e s a d e ep p u r p le c o l o r . T h is c o n d i t i o n i s fo u n d i n
44
b o th jh ie id e s and T r i t u r o s . However i n T yphlom olge, w here
s t a i n i n g was done w i t h th e same r e a g e n t a s i n th e o t h e r two
s p e c im e n s , t h e mucous s t a i n s l i g h t l y w ith a f i n e h a i r - l i k e
p u r p l e n e tw o rk ru n n in g th r o u g h i t , and no l a r g e m ucinogen
g r a n u l e s a re o b se rv e d i n the c y to p la s m . A p p a re n tly th e
d i f f e r e n c e i n s t a i n i n g i s due t o a change i n th e c h e m ic a l
c o n t e n t s of th e mucous a s the s e c r e t i o n d e v e lo p s . M oreover,
i n Typhlom olge many of t h e g o b l e t c e l l s a r e o b se rv e d to
c o n t a i n a lm o s t no c y to p la s m a n i the n u c le u s i s on th e edge
o f t h e p o r t i o n of t h e c e l l t h a t i s f i l l e d w i t h mucous. T h is
c o n d i t i o n i s not fou nd by th e w r i t e r i n the o t h e r two
a n im a l s . The mucous s e c r e t i o n c a u s e s th e s i d e s o f t h e c e l l s
t o b u lg e , and in many i n s t a n c e s p r o j e c t i n t o the i n t e s t i n a l
lum en. The w a l l of t h e s e c e l l s n e x t the lum en i s t h i n and
l a c k s the s t r i a t i o n found i n th e colum nar e p i t h e l i u m and is
s a i d by Bremer t o r u p t u r e i n man # i e n th e c e l l s become f u l l
o f mucous.
In t h e w e ll d e v e lo p e d g o b l e t c e l l t h e n u c le u s i s
pu sh e d downward by th e mass o f m ucig en, which the c e l l
s e c r e t e s , and l i e s i n th e p r o to p la s m composing th e c h a l i c e of
t h e g o b l e t . The r e g i o n where the n u c le u s i s l o c a t e d i s
n a r r o w e r th a n t h a t a b o v e, a n d below t h e n u c le u s th e p r o t o
p lasm i s s t i l l more a t t e n u a t e d fo rm in g t h e s te m o f th e
g o b l e t w h ile the end i s a f f i x e d to th e b asem ent membrane
45
and o f t e n w idens a l i t t l e t o s im u la te t h e ”f o o t ’^ o f a g o b le t.
The shape d ep en d s upon th e amount o f s e c r e t i o n and th e
p o s i t i o n of t h e c e l l and t h e expanding mass o f m ucigen
c a u s e s t h e w a l l s t o b u lg e on a l l s i d e s i n t o c h a r a c t e r i s t i c
g o b l e t form.
A ccording to Cowdry, (1 9 2 6 ), h i s t o l o g i s t s advance two
t h e o r i e s t o a c c o u n t f o r t h e o r i g i n o f g o b l e t c e l l s , one b e in g
t h a t th e y d e v e lo p from a n in d e p e n d e n t e le m e n t, r e s e r v e d from
th e p r i m i t i v e en to d erm of th e d i g e s t i v e t r a c t f o r t h i s
p u rp o s e w h ile t h e s e c o n d t h e o r y c la im s t h a t th e y e v o lv e from
p r i m i t i v e c e l l s . He i s i n c l i n e d tow ard t h e se c o n d th e o r y f o r
two r e a s o n s , nam ely: ( l ) t h e r e i s a m o r p h o lo g ic a l re s e m b la n c e
o f young g o b l e t c e l l s t o p r i m i t i v e p r i n c i p a l c e l l s ; (2) th e
number o f g o b l e t c e l l s s p e e d i l y i n c r e a s e d u rin g s t a r v a t i o n .
In a d d i t i o n Cowdry c la im s t h a t e i t h e r g o b l e t c e l l s have
m u l t i p l i e d or t h a t e p i t h e l i a l c e l l s of t h a t r e g i o n have been
t r a n s f o r m e d i n t o g o b l e t c e l l s and t h a t t h e r e i s some e v id e n c e
to s u p p o r t the f a c t t h a t g o b l e t c e l l s r e v e r t to p r i n c i p a l
c e l l s .
B oth i n A neid es and T r i t u r o s th e e p i t h e l i a l c e l l s a r e
n a rro w , t a l l and c o lu m n a r, w h ile i n Typhlom olge th e y v a ry
from t a l l to ^ o r t colum nar to c u b o id a l, - c u b o id a l b e in g
th e m ost common ty p e i n th e l a r g e i n t e s t i n e . These c e l l s
e x h i b i t a t h i c k e n e d , f r e e , ( F ig . 1 4 ), s u r f a c e or c u t i c u l a
n e x t th e lumen and show a c r o s s s t r i a t i o n s i m i l a r to th o se
46
o f th e f r o g . However, t h i s c o n d i t i o n is not so a p p a r e n t i n
Typhlom olge a s i n t h e o t h e r two sp e c im e n s . In Typhlom olge
th e s t r i a t i o n s a p p e a r i n th e duodenum a n d b e g in to fa d e o u t
i n th e ile u m , M iile the l a r g e i n t e s t i n a l e p i t h e l i a l c e l l s a r e
f r e e of them a l t o g e t h e r . M oreover, th e c u t i c u l a i s t h i c k e r
i n some a r e a s th an i n o t h e r s . Bremer s t a t e s t h a t th e
s t r i a t i o n s a r e c o n s id e r e d to h e p r o to p la s m ic p r o c e s s e s
lo d g e d i n p o r e s and t h e w r i t e r i s i n c l i n e d to a g re e w i t h t h i s
c o n c l u s i o n , b e c a u se on many c r o s s s e c t i o n s w here th e m ic ro
tome c u t th r o u g h t h e s e p o r e s th e p r o c e s s e s a p p e a r s i m i l a r t o
c i l i a . The n u c l e i of t h e s e c e l l s a r e s p h e r i c a l or s l i g h t l y
f l a t t e n e d i n Typhlom olge and g r e a t l y f l a t t e n e d i n T r i t u r o s ,
w h ile i n A neid es an i n t e r m e d i a t e s t a t e i s fo u n d , - n u c l e i
o c c u r r i n g n e i t h e r so s p h e r i c a l as i n Typhlomolge o r as g r e a t l y
e lo n g a te d a s i n T r i t u r o s . E x ce p t w here p l i c a t i o n s o c c u r , th e
e p i t h e l i u m i s sim p le th ro u g h o u t th e i n t e s t i n e , - u s u a l l y one
c e l l i n t h i c k n e s s . The e p i t h e l i u m c o v e r in g th e p l i c a t i o n s
assum es the a p p e a ra n c e o f s t r a t i f i e d colum nar ty p e i n some
p l a c e s . S m all l e u c o c y t e s a r e fo u n d f r e q u e n t l y among th e
e p i t h e l i a l c e l l s .
Musc u l a r i s m ucosae. The m u s c u la r is m ucosa, so w e l l
d e v e lo p e d i n h i g h e r v e r t e b r a t e s , i s not so a p p a re n t i n t h e s e
s a la m a n d e r s . I t c o n s i s t s o f o n ly one t o f o u r c i r c u l a r m u scle
f i b e r s and l o n g i t u d i n a l m u sc le f i b e r s i n t h e duodenum o f
A neid es and T r i t u r o s . T his l a y e r is n o t c o n tin u o u s aro und
47
th e o rg a n a s w ide sp a c e s o c cu r w here no f i b e r s o f t h i s ty p e
e x i s t . These s l e n d e r f i b e r s in v a d e the p l i c a e w here th e y
a p p e a r to be num erous and extend up and down t h e s e f o l d s o f
t h e duodenum o f b o t h A neides and T r i t u r o s , b u t th e y a r e n o t
o b s e rv e d i n Typhlom olge. T h is c o n d i t i o n may be due to th e
f u s i n g of th e m u a c u la r is mucosae and the m u s c u la r is e x te r n u s .
In t h e p o s t e r i o r h a l f o f th e ile u m of b o t h T r i t u r o s and
A n eid es no m u s c u la r is mucosa i s o b s e rv e d , n e i t h e r i s i t
fo u n d i n th e l a r g e i n t e s t i n e of the t h r e e form s s t u d i e d . In
some c r o s s s e c t i o n s of T r i t u r o s and A n e id e s, l o n g i t u d i n a l
f i b e r s of th e m u s c u la r is mucosae o c c u r i n s m a ll r e s t r i c t e d
a r e a s and t h i s l a y e r i s n o t c o n tin u o u s aro u n d t h e o rg a n . I t
i s a l t o g e t h e r m is s in g i n t h e v e n t r a l w a l l. In Typhlom olge
t h i s l a y e r i s n o t p r e s e n t and th e l o n g i t u d i n a l l a y e r i s much
n a r r o w e r th a n the c i r c u l a r one i n m ost c a s e s b u t w here
a g g r e g a t i o n s of f i b e r s a r e fo u n d , a s many a s s i x or e i g h t
can be c o u n ted i n one g ro u p .
Submucosa - G la n d s . The submucosa i s a t h i n c o n n ec
t i v e t i s s u e l a y e r in v^hich t h e i n t e s t i n a l g la n d s a r e l o c a t e d
(F ig . 1 5 ). In a l l t h r e e form s i t s t a i n s a d e e p e r r e d th a n
th e c o n n e c tiv e t i s s u e o f o t h e r r e g i o n s . The g la n d s a r e
sim p le c o n s i s t i n g of an a g g r e g a t e of c e l l s w i t h no lumen
a p p a r e n t . N o thin g com parable to th e c r y p t s o f L ie b e rk u h n of
h i g h e r v e r t e b r a t e s o c c u rs i n th e s a la m a n d e rs s t u d i e d , h en ce
F i g . 15. Typhlom olge r a t h h u n i
P o s t e r i o r p o r t i o n of ile u m ,
d o r s a l s i d e .
G ross s e c t i o n . X355
EP E p it h e l i u m
GÜ G o b le t c e l l
CA C a p i l l a r y
G Lymph g la n d i n subm ucosa
CM C i r c u l a r m uscle l a y e r
LM L o n g i t u d i n a l m u sc le l a y e r
S S e r o s a
48
c - o
L M
C M
FIG.15
F i g . 16. Typhlom olge r a t h h u n l
Duodenum showing d e t a i l e d s t r u c t u r e
o f a p l i c a t i o n and w a ll of th e i n t e s t i n e .
Gross s e c t i o n . X 355
GU — G oblet c e l l
EP E p ith e liu m
CA — C a p i l l a r y
SM Submucosa
CM C i r c u l a r m uscle l a y e r
LM — L o n g it u d i n a l m uscle l a y e r
G Lymph g la n d
S S e r o s a
49
GO
ET
OC
U t
O M
SM
FIG.16
50
t h e i n t e s t i n a l g l a n d s a r e b e l i e v e d n o t t o empty i n t o th e
b o tto m s of t h e s e o r y p ts a s th e y do i n mammals. A ggrega
t i o n s o f t h e s e g la n d s v a ry i n numbers from t h r e e t o f i v e or
s i x on one c r o s s s e c t i o n . In one c r o s s s e c t i o n of t h e s e
g la n d s o f the duodenum f i v e to f i f t e e n c e l l s can b e c o u n te d
i n e a c h g la n d . T hese c e l l s a r e r e a d i l y d i s t i n g u i s h e d from
e p i t h e l i a l by t h e i r d a r k ly s t a i n i n g , s m a l l e r and more
s p h e r i c a l n u c l e i and by th e s i z e o f t h e c e l l i t s e l f , w h ich
i s much s m a l l e r and p o ly g o n a l i n â i a p e . A lso th e c y to p la s m
s t a i n s d a r k e r th an t h a t of th e e p i t h e l i a l c e l l s . T hese
s im p le g la n d s do n o t have lymph n o d u le s and t h e c e n t e r o f t h e
s m a l l e r a g g r e g a t i o n s of c e l l s d o e s n o t c o n t a i n th e l i g h t e r
a r e a of more complex g la n d s t h a t a r e fo u n d i n h i g h e r v e r t e
b r a t e s . U s u a l l y a s many a s e i g h t s e p a r a t e g la n d s o c c u r i n
one c ro s s s e c t i o n o f th e duodenum, b u t i n some s e c t i o n s th e y
form an a lm o st c o n tin u o u s band arou nd th e i n t e s t i n e , w h ile
i n o t h e r s t h e r e may be o n ly t h r e e o r f o u r . The g r e a t e s t
number alw ay s o c c u rs on the d o r s a l s i d e vdiich i s d e te r m in e d
by t h e a tta c h m e n t of th e m e s e n te ry . These g l a n d s may be
com parable to th e B r u n n e r 's g la n d s i n th e man, b u t they o c c u r
much more f r e q u e n t l y and a r e s im p le r i n s t r u c t u r e . These
lymph g la n d s a r e f o u n d a l s o i n th e re m a in d e r of th e s m a ll
i n t e s t i n e of t h e t h r e e a n im a ls s t u d i e d and a r e alw ays i n th e
subm ucosa. In th e l a r g e i n t e s t i n e of Typhlom olge th e y a r e
n o t o b s e r v e d , w h ile i n th e o t h e r two, th e y a r e n o t so
61
num erous i n the a n t e r i o r p o r t i o n . They te n d to d e c r e a s e i n
number and f i n a l l y d i s a p p e a r a s t h e p o s t e r i o r end of t h e
l a r g e i n t e s t i n e i s a p p ro a c h e d .
P l i c a t i o n s . As i n th e stom ach o f the s p e c i e s
s t u d i e d th e submucosa o f th e i n t e s t i n e i s throw n i n t o
num erous p l i c a t i o n s ( P i g . 1 6 ) , which a r e c o v e re d by th e
e p i t h e l i a l c e l l s . J u s t p o s t e r i o r to t h e p y l o r u s th e s e f o l d s
ta k e th e form o f an i r r e g u l a r n e tw o rk . In A n e id e s, p o s t e r i o r
to t h i s n e tw o rk , p l i c a e w hich a re l a r g e and sem i l u n a r i n
shape a r e a r r a n g e d i n two s e r i e s w h ich emerge from th e
l a t e r a l w a lls and e x te n d d o r s o v e n t r a l l y f o r a d i s t a n c e o f
a p p r o x im a te ly two mm. T h is c o n d i t i o n oc c u rs a l s o i n
Typhlom olge and T r i t u r o s and i s s i m i l a r t o t h a t fo u n d i n th e
f r o g . A p p a re n tly t h e s e p l i c a t i o n s form p o c k e ts which keep
t h e fo o d from flo w in g b a c k i n t o th e sto m a c h .
As one p ro c e e d s to w a rd th e p o s t e r i o r p o r t i o n o f th e
s m a ll i n t e s t i n e , th e p l i c a e become more r e g u l a r l y a r r a n g e d
and t h e f o l d s a r e m o s tly l o n g i t u d i n a l i n T r i t u r o s and
T yphlom olge. At f i r s t th e p l i c a t i o n s a r e e x tre m e ly t a l l and
p o i n t e d when t h e s m a ll i n t e s t i n e i s enpty o f fo o d . These
f o l d s v a ry i n h e i g h t . In A neides th e m ucosal c e l l s c o u n te d
from t h e p o i n t w here t h a t l a y e r d i p s dov/n b e tw e e n the p l i c a e
to th e t i p of the f o l d num bers fro m tw e lv e to f i f t y - o n e
52
c e l l s , w h ile i n t h e jejunu m e le v e n to s e v e n t y - f i v e c e l l s may
he c o u n te d . In t h e ile u m of th e same a n im a l th e c e l l s c o v e r
in g t h e p l i c a t i o n s v a ry fro m s e v e n to t h i r t y - o n e . In T r i t u r o s
com parable v a r i a t i o n s i n h e ig h t o f p l i c a t i o n s o c c u r; i n th e
duodenum, tw e n ty t o f i f t y - t w o c e l l s ; i n th e jejunu m , t h i r t y -
e i g h t to s i x t y - f i v e c e l l s ; i n the ile u m , f o u r t e e n to t h i r t y -
se v e n c e l l s . The same d i f f e r e n t i a t i o n o c c u rs i n Typhlom olge
b u t th e p l i c a t i o n s a r e lo w e r p r o b a b ly due to th e s m a ll s i z e
o f th e a n im a l. H ere p l i c a t i o n s i n th e duodenum n e v e r m eas
u r e more th a n t h i r t e e n c e l l s w h ile th e jejunum m ea su re s a s
many as tw e n ty -tw o c e l l s c o u n te d fro m th e lo w e s t p o i n t b e
tw een p l i c a t i o n s to th e h i g h e s t t i p w h ile i n t h e ile u m th e y
v a r y from s e v e n to t h i r t y - o n e c e l l s .
In r e s t r i c t e d r e g i o n s l a t e r a l p l i c a e f u s e w ith
l o n g i t u d i n a l ones i n T r i t u r o s and Typhlom olge b u t i n A neides
th e subm ucosa i s th ro w n i n t o l o n g i t u d i n a l and l a t e r a l f o l d s
w h ich f u s e w ith each o t h e r and form n e tw o rk s f o r a lm o s t th e
e n t i r e l e n g t h of the s m a ll i n t e s t i n e . On a lm o st e v e ry c r o s s
s e c t i o n of A n eid es exam ined t h i s c o n d i t i o n i s a p p a r e n t .
A lth o u g h th e p l i c a t i o n s v a r y i n number as many as e le v e n
f o l d s can b e c o u n te d on some c r o s s s e c t i o n s w h i l e o n ly t h r e e
may o c c u r on o t h e r s . T hese p l i c a e a r e found f o r t h e e n t i r e
d i s t a n c e aro und the o rg a n on some c ro s s s e c t i o n s and u s u a l l y
th e y a r e t a l l e s t on t h e d o r s a l s i d e . Some of them have l e a f -
53
l i k e p r o j e c t i o n s i n A n e id e s.
As t h e p o s t e r i o r p o r t i o n of t h e s m a ll i n t e s t i n e i s
a p p ro a c h e d the p l i c a t i o n s become s h o r t e r and th e ends b l u n t .
They do n o t o c c u r w ith the same r e g u l a r i t y . On some c r o s s
s e c t i o n s o f A neid es p l i c a e a r e e n t i r e l y a b s e n t on th e v e n t r a l
and l a t e r a l w a l l s v h i l e i n o t h e r s , p l i c a e o c c u r r e g u l a r l y
around the i n t e s t i n e . F o r th e e n t i r e l e n g t h of th e i n t e s t i n e
o f A neides t h e r e i s o b se rv e d a l a r g e f o l d on th e d o r s a l s i d e .
The same c o n d i t i o n i s o b se rv ed i n T r i t u r o s . In T yphlom olge,
p o s t e r i o r to t h e s e m i - l u n a r f o l d s , th e p l i c a t i o n s a r e t a l l
and n um erou s. Sometimes a s many as t e n o c c u r i n one c r o s s
s e c t i o n b u t as one p ro c e e d s p o s t e r i o r l y t h e y become b l u n t e r ,
and s h o r t e r , and l e s s num erous. As few as t h r e e p l i c a t i o n s
o c c u r and t h e r e i s v e ry l i t t l e c o n n e c tiv e t i s s u e p r e s e n t . In
Typhlom olge th e subm ucosa fo rm s a v e r y t h i n l a y e r b e in g a b o u t
o n e - e i g h t h to o n e - f o u r t h t h e w id th of t h e e x t e r n a l m uscle
l a y e r , w h ile i n T r i t u r o s t h e subm ucosa i s w id e r th a n th e
m u s c u l a r i s e x te r n u s i n p l a c e s . In a l l t h r e e s p e c i e s s t u d i e d
t h e p l i c a t i o n s d i v i d e th e s m a ll i n t e s t i n e i n t o w e l l d e f i n e d
r e g i o n s as f o l l o w s : ( l ) a sm a ll r e g i o n fo rm in g a n e tw o rk of
l a t e r a l and l o n g i t u d i n a l f o l d s p o s t e r i o r t o the p y l o r u s ;
(2) a s h o r t r e g i o n of t h e s e m i- l u n a r f o l d s ; ( 3 ) a r e g i o n of
e x tre m e ly t a l l p l i c a t i o n s w here f u s i n g of l a t e r a l f o l d s o ccu r
a s w e l l as l o n g i t u d i n a l f o l d s ; (4) a r e g i o n w here t h e f o l d s
54
a r e s h o r t e r and b l u n t e r and w here th e p l i c a e may n o t o c c u r
c o n ti n u o u s l y a ro u n d th e o r g a n 's e n t i r e c ir c u m f e r e n c e .
In h i g h e r v e r t e b r a t e s t h e i n t e s t i n a l g la n d s w hich
empty i n t o t h e c r y p t s o f l i e b e r k u h n a r e found i n t h e mucosa
and e x te n d down i n t o t h e subm ucosa o f t h e duodenum and
jeju n u m . In the l a t t e r , th e g la n d s a r e s h o r t e r and s e r v e as
one of t h e means of l o c a t i n g the jeju n u m , b u t i n t h e s e s a l a
m an d ers, none of t h e s e g la n d s o c c u r; I f t h e i n t e s t i n e s o f
s a la m a n d e rs may be s a i d to be d iv id e d i n t o duodenum,
jeju n u m , and ile u m s i m i l a r to h ig h e r v e r t e b r a t e s , t h e d i s
t i n c t i o n must be b a s e d e n t i r e l y on th e h e i g h t of t h e
p l i c a t i o n s p r e v i o u s l y m e n tio n e d . The duodenum p o s s e s s e s th e
t h i n l e a f - l i k e p l i c a t i o n s w hich a r e c l o s e t o g e t h e r and te n d
t o e n c i r c l e th e o rg an fo rm in g l a t e r a l and l o n g i t u d i n a l
b r a n c h e s which f u s e r e p e a t e d l y w i t h one a n o t h e r . The
jejunu m p o s s e s s e s th e t a l l e s t p l i c a t i o n s , w h ile th e ile u m ,
w here the p l i c a e a r e low er and f u r t h e r a p a r t and come to an
end a t th e a n t e r i o r end of the l a r g e i n t e s t i n e form s t h e
t h i r d d i v i s i o n . These l a r g e f o l d s p ro d u c e a g r e a t a b s o r p
t i v e s u r f a c e th ro u g h w hich t h e n u t r i t i o n fro m the d i g e s t e d
fo o d can be t a k e n up by th e b lo o d s tr e a m and t r a n s p o r t e d t o
d i f f e r e n t p a r t s of th e body. T here i s no a b r u p t c h an g e ,
how ever, i n s i z e o r a rra n g e m e n t o f p l i c a t i o n s i n th e
i n t e s t i n e of t h e s e s a la m a n d e r s . At f i r s t t a l l p o i n t e d
55
p l i c a t i o n s o c c u r i n t e r s p e r s e d w i t h th e ty p e t h a t i s t y p i c a l
o f th e duodenum u n t i l a c o n d i t i o n is r e a c h e d w h ere a l l th e
p l i c a t i o n s a r e t a l l and p o i n t e d . The same c o n d i t i o n i s
fo u n d a t t h e a n t e r i o r p o r t i o n o f th e ile u m w here t a l l
p l i c a t i o n s o c c u r w ith s h o r t e r , b l u n t e r ty p e u n t i l n o t h in g b u t
th e s h o r t e r , b l u n t type i s fo u n d .
M u s c u la r is e x te r n u s - L o n g i t u d i n a l l a y e r . The
m u s c u la r is e x te r n u s of the s m a ll i n t e s t i n e c o n s i s t s o f two
t h i n l a y e r s of f i b e r s . Most o f th e d i s t a n c e aroun d th e
i n t e s t i n e o f Typhlom olge and A n e id e s, the l o n g i t u d i n a l f i b e r s
a r e m is s in g b u t i n a few p l a c e s t h e y o c c u r i n l a r g e clumps or
c o n tin u o u s f o r o n ly a s h o r t d i s t a n c e i n r e s t r i c t e d a r e a s
u s u a l l y i n t h e d o r s a l w a l l . The clumps may c o n t a i n f i v e or
s i x f i b e r s b u t i n o t h e r p l a c e s th e l o n g i t u d i n a l l a y e r i s only
two or t h r e e c e l l s t h i c k . In T r i t u r o s th e l o n g i t u d i n a l
l a y e r i s w e ll d e v e lo p e d and co nt inuous a ro u n d t h e o rg a n , b u t
i s n o t so t h i c k as t h e c i r c u l a r l a y e r . I t a l s o v a r i e s i n
t h i c k n e s s fro m one or two f i b e r s on th e v e n t r a l w a l l t o f o u r
o r s i x on th e d o r s a l s i d e .
C i r c u l a r m uscle l a y e r . I n a l l t h r e e s p e c i e s t h e
c i r c u l a r m u sc le l a y e r s a r e c o n tin u o u s a ro u n d the s m a ll
i n t e s t i n e b u t v a r i e s i n w id th fro m two o r t h r e e f i b e r s on th e
v e n t r a l and l a t e r a l s i d e s t o f i v e to e i g h t on th e d o r s a l a id e .
The n u c l e i of t h e s e c e l l s a r e alw ays s t e l l a t e in s h a p e . The
whole m u s c u la r w a l l i s n a rro w .
F i g . 17. Typhlom olge r a t h h u n l
V e n t r a l w a ll of c o lo n .
Gross s e c t i o n . % 355
s:.i
G A
G!1
E p ith e liu m
Submucosa
C a p i l l a r y
C i r c u l a r musc le l a y e r
S eros a
56
FIG.17
57
V I I . LARGE IRTESTIRE
The l a r g e i n t e s t i n e i s c o n tin u o u s w i t h th e c a u d a l end
o f t h e sm a ll i n t e s t i n e and l i e s i n t h e c a u d a l end o f th e
coelom . I t i s sim p le i n s t r u c t u r e i n a l l t h r e e s p e c i e s
s t u d i e d . The mucosa i s o n ly one c e l l i n t h i c k n e s s . ( F i g . 1 7 ).
B o th g o b l e t c e l l s and sim p le e p i t h e l i a l c e l l s s i m i l a r to
t h o s e of th e s m a ll i n t e s t i n e o c c u r. The subm ucosa is narrow
and i n t h e p o s t e r i o r end no p l i c a t i o n s a r e o b s e rv e d . The
e x t e r n a l m u sc le l a y e r c o n s i s t s a lm o s t e n t i r e l y o f c i r c u l a r
f i b e r s o n ly one t o f o u r or f i v e i n t h i c k n e s s . In p l a c e s
w here t h e s t r u c t u r e s a r e m ost s im p le , t h e e n t i r e w id th o f
t h e i n t e s t i n a l w a ll i s o n ly f o u r to s i x c e l l s i n t h ic l m e s s
c o u n ti n g c e l l s i n a l l f o u r l a y e r s . L o n g it u d i n a l m uscle
f i b e r s o c c u r, b u t e n t i r e l y fa d e o u t f o r l a r g e s p a c e s . Ro
i n t e s t i n a l g la n d s a r e fo u n d i n th e p o s t e r i o r p o r t i o n of th e
l a r g e i n t e s t i n e i n any of th e s p e c i e s o b s e rv e d .
The s e r o s a f o r t h e e n t i r e l e n g t h of th e i n t e s t i n e i s
s i m i l a r t o t h a t of t h e esophagus or stom ach of t h e s a l a
m anders s t u d i e d and i s o n ly one c e l l i n t h i c k n e s s .
The c lo a c a fo rm s th e t e r m i n a l p o r t i o n o f th e a lim e n
t a r y c a n a l . The u r o g e n i t a l sy ste m e m p tie s i n t o i t a s v /e ll as
th e i n t e s t i n e .
58
V I II . DISCUSSlOR
The amount o f d i s c u s s i o n i s l i m i t e d due t o th e f a c t o f
t h e s c a r c i t y o f l i t e r a t u r e on c l o s e l y r e l a t e d fo rm s.
E so p h a g u s . The esophagus of sa la m a n d e rs i s sh o rt and
r e m a rk a b ly d i s t e n s i b l e . The i n n e r s u r f a c e i s th ro w n i n t o
l o n g i t u d i n a l f o l d s w hich c o n ti n u e i n t o t h e stom ach and i s
s i m i l a r t o th e c o n d i t i o n fo u n d i n f i s h e s and t h e f r o g .
R o g ic k (1931) s t a t e s t h a t t e n m ajor l o n g i t u d i n a l f o l d s o c cu r
i n t h e t e l e o s t f i s h , Campostoma anomalum. B lak e (1930) f i n d s
t h i s c o n d i t i o n i n th e s e a b a s s , C e n t r o p i e s t e s s t r i a t u s . These
f o l d s w h ich v a r y w i t h th e s p e c i e s a r e c h a r a c t e r i z e d by a t h i c k
c o v e r in g ox s t r a t i f i e d e p i t h e l i u m . T a s te buds a r e fo u n d on
th e t i p s o f th e s e f o l d s i n some f i s h e s , b u t t h i s c o n d i t i o n
h a s n o t b e e n o b se rv e d i n t h e s e sa la m a n d e rs n o r r e p o r t e d i n th e
f r o g .
M ucosa. Two ty p e s of c e l l s o c c u r i n th e e p i t h e l i u m : -
g o b l e t and colum nar* I n sa la m a n d e rs the c o lu m n ar c e l l s a r e
c i l i a t e d , b u t i n man t h e s e c e l l s a r e known to be c i l i a t e d o n ly
i n t h e embryo. Wide v a r i a t i o n in number and l o c a t i o n of
mucous c e l l s o c c u r s . R o gick s t a t e s t h a t i n c e r t a i n f i s h e s th e y
a r e l o c a t e d on ly on th e s i d e s of th e p l i c a t i o n s . I n T r i t u r o s
and Typhlom olge how ever, mucous c e l l s a re o b s e rv e d anyw here
on th e l o n g i t u d i n a l f o l d s i n t e r s p e r s e d among th e colum nar
59
c e l l s , w h ile i n A neidea a l l th e e p i t h e l i a l c e l l s i n t h e
a n t e r i o r esophagus a r e mucous.
In th e human b e i n g s u p e r f i c i a l and deep e s o p h a g e a l
g la n d s o c c u r . The d e ep ones p e n e t r a t e t h e suhmucosa and a r e
fo u n d t h r o u g h o u t th e e n t i r e l e n g t h of th e o rg a n . The s u p e r
f i c i a l occur i n two r e s t r i c t e d a r e a s l o c a t e d a t t h e a n t e r i o r
and p o s t e r i o r ends o f th e e so p h a g u s. In th e t h r e e
s a la m a n d e rs h e r e s t u d i e d , e s o p h a g e a l g l a n d s a r e fo u n d o n ly
i n a r e s t r i c t e d r e g i o n i n th e p o s t e r i o r end. Bohle (1931)
s t a t e s t h a t e s o p h a g e a l g la n d s o c c u r j u s t b e f o r e t h e stom ach
o f Hana and 3 u fo b u t do n o t o c c u r i n v a r i o u s more p r i m i t i v e
S a l i e n t i a o r i n c e r t a i n U r o d e le s .
B lak e (1 9 3 0 ), R ogick (1 9 3 1 ), and S u r r a r r e r (1931)
s t a t e t h a t i n f i s h th e musc u l a r i s e x te r n u s i s s t r i a t e d , b u t
i n t h e sa la m a n d e rs h e r e exam ined t h i s c o n d i t i o n v a r i e s . In
A n eid es and T r i t u r e s th e a n t e r i o r p o r t i o n i s s t r i a t e d and
th e p o s t e r i o r h a s o n ly smooth m uscle f i b e r s , w h ile i n
Typhlom olge o n ly sm ooth o c c u r . The m u s c u la r is e x te rn u s o f
s a la m a n d e rs i s t h i n a n d c o r r e s p o n d s t o t h e c o n d i t i o n r e
p o r t e d f o r f i s h e s and f r o g s . I t i s g e n e r a l l y i n t e r p r e t e d
t h a t t h e s e a n im a ls depend upon th e p e r i s t a l t i c a c t i o n of th e
m u sc le f i b e r s to c a r r y t h e fo o d to t h e stom ach.
60
Stom ach. The e p i t h e l i a l c e l l s o f t h e stom ach a r e
sim p le colum nar i n b o t h a m p h ib ian s and f i s h e s , b u t wide
v a r i a t i o n s o c c u r i n t h e g a s t r i c g l a n d s . B la k e (1930) s t a t e s
t h a t t h e g e n e r a l a rra n g e m e n t of g a s t r i c g la n d s i n f i s h e s i s
t o fo rm s t r a i g h t t u b e s . B i f u r c a t i o n o f th e b l i n d ends to
form compound g la n d s was o b s e rv e d b u t was u n u s u a l . He
f u r t h e r found t h a t t h e number of t h e s e g la n d s opening i n t o
e ac h c r y p t may r u n as h ig h a s s i x or m ore, b u t th e a v e r a g e
i s much lov/er. A lso g la n d s o f th e c a r d i a c r e g i o n i n f i s h e s
a r e l o n g e r th a n i n t h e p y l o r ic * These c o n d i t i o n s c o rre s p o n d
t o t h a t o b s e rv e d in T yphlom olge. In A neides and T r i t u r e s
t h e g la n d s a r e u s u a l l y b r a n c h e d , i n d i c a t i n g a h i g h e r d e g re e
o f s p e c i a l i z a t i o n th a n r e p o r t e d i n f i s h e s . R o g ick (1931)
s t a t e s t h a t t h e f i s h , Campostoma anomalum, h a s no t r u e
sto m ach . I t s p l a c e i s t a k e n by an i n t e s t i n a l b u lb and t h a t
no m u l t i - c e l l u l a r g la n d s of t h e g a s t r i c or i n t e s t i n a l ty p e
o c c u r i n t h e b u lb or i n t e s t i n e p r o p e r .
A m u s c u l a r i s m ucosa i s p r e s e n t i n f r o g s and s a l a m a n d e r s ,
b u t a b s e n t i n f i s h e s . A p p a r e n tly w ith t h e demand f o r
g r e a t e r p e r i s t a l t i c a c t i o n t h e s e f i b e r s have d i f f e r e n t i a t e d .
T hree m u sc le l a y e r s a r e known to o c c u r i n t h e human
m u s c u l a r i s e x t e r n u s , b u t o n ly two a r e fo u n d i n s a la m a n d e r s .
B lake o b s e rv e d l o c a l t h i c k e n i n g s i n th e e x t e r n a l m uscle l a y e r
o f f i s h e s , a c o n d i t i o n w hich o c c u rs th r o u g h o u t th e e n t i r e
61
l e n g t h of th e d i g e s t i v e t r a c t o f s a la m a n d e rs exam ined, b u t
w hereas b o t h s t r i a t e d and u n s t r i a t e d f i b e r s o c c u r i n t h e
c i r c u l a r m u sc le of f i s h e s , o n ly u n s t r i a t e d a r e fo u n d i n
s a la m a n d e r s . I n f i s h e s t h e c i r c u l a r i s i s s e p a r a t e d from t h e
t h i n l o n g i t u d i n a l l a y e r by c o n n e c ti v e t i s s u e c o n t a i n i n g
b lo o d v e s s e l s , b u t i n sa la m a n d e rs a subm ucosa i s p r e s e n t
w h ich c o n t a i n s th e b l o o d v e s s e l s . M oreover t h e l o n g i t u d i n a l
m u scle l a y e r i s t h i n i n f i s h e s and c o r r e s p o n d s to th e
c o n d i t i o n found i n s a la m a n d e rs .
I n t e s t i n e . V/hile a m p h ib ia n s have f o u r l a y e r s i n th e
i n t e s t i n a l w a l l t y p i c a l o f v e r t e b r a t e s , f i s h e s , a c c o rd in g t o
S u r r a r r e r (1931) and R o g ick (1 9 3 1 ), have o n ly t h r e e , th e
subm ucosa b ein g a b s e n t . In t h e lo w er v e r t e b r a t e s th e i n
t e s t i n e shows l i t t l e marked h i s t o l o g i c a l d i f f e r e n t i a t i o n a t
th e v a r i o u s l e v e l s b u t i n the sm a ll i n t e s t i n e th e subm ucosal
f o l d s a r e more num ero us, th e lum en s m a l l e r , and th e w a l l
p r o p o r t i o n a l l y t h i c k e r . Ro i n t e s t i n a l g la n d s su c h a s o c c u r
i n man a re f o u n d i n e i t h e r f i s h e s o r anqohibians, however
lymph g la n d s a r e p r e s e n t o n ly i n th e subm ucosa of a m p h ib ia n s .
The o u t e r p o r t i o n o f t h e e x t e r n a l m uscle l a y e r of th e i n
t e s t i n e i n b o t h a m p h ib ia n s and f i s h e s i s t h i n n e r th a n th e
c i r c u l a r l a y e r . T here i s no a b ru p t change betw een esophagus
and stom ach o r b etw een stom ach and i n t e s t i n e i n e i t h e r f i s h
o r a m p h ib ia n s . T h is s u p p o r t s t h e t h e o r y t h a t i n i t s
e v o l u t i o n a r y d e v e l o p m e n t t h e d i g e s t i v e t r a c t was a t one
t i m e a h o rn o g e n io u s s t r a i g h t t u b e .
63
IX. S U M M A R Y
1 . T h ree s a la m a n d e rs r e p r e s e n t i n g s e p a r a t e g e n e r a have
b e en exam ined #nd t h e t i s s u e s of t h e d i g e s t i v e t r a c t s
a r e fo u n d t o be n o t so h i g h ly d i f f e r e n t i a t e d a s th o s e
o f h i g h e r v e r t e b r a t e s .
E. Pour l a y e r s of t i s s u e t y p i c a l o f v e r t e b r a t e s a r e
p r e s e n t i n th e d i g e s t i v e w a l l. The s t r u c t u r e o f t h e s e
l a y e r s i n T yphlom olge i s s im p le r th a n th o s e i n A neides
or T r i t u r o s i n d i c a t e s a c o r r e l a t i o n w ith th e r e s t r i c
t e d and u n u s u a l h a b i t a t .
3 . Ro a b r u p t change o c c u rs i n th e c e l l s t r u c t u r e o f th e
w a l l b e tw e e n t h e e so p h ag u s and stom ach o r th e l a t t e r
and the i n t e s t i n e i n t h e s e fo rm s.
4 . T a l l colum nar c e l l s c o n s t i t u t e th e m ucosal e p i t h e l i u m
o f T_i. t o r o s u s and ^ l u g u b r i s l u g u b r i s , w h ile
c u b o id a l and lovv^ colum nar c e l l s o c c u r i n Tj_ r a t h b u n i .
5. G o b le t c e l l s occur i n t h e eso p h ag u s an d i n t e s t i n e b u t
a r e n o t p r e s e n t i n t h e stom ach i n any of t h e s e t h r e e
sp e c im e n s . The c h e m ic a l c o n te n t of t h e s e g o b l e t c e l l s
u n d o u b te d ly changes as th e s e c r e t i o n a c c u m u la te s as
in f.c a te d by s t a i n i n g r e a c t i o n s . A l l th e e p i t h e l i a l
c e l l s l i n i n g t h e esophagus i n each of t h e s e t h r e e
64
form s a r e c i l i a t e d e x c e p t t h e g o b l e t c e l l s .
6 . In ^ l u g u b r i s l u g u b r i s th e m u co sal e p i t h e l i u m
c o n s i s t s e n t i r e l y o f mucous c e l l s w h ile i n th e o t h e r
two fo rm s, g o b l e t c e l l s a r e i n t e r s p e r s e d among t a l l
co lum nar e p i t h e l i a l c e l l s .
7. The e x t e r n a l m uscle l a y e r o f th e e so p h a g u s o f
T. t o r o s u s and ^ r a t h b u n i i s t h i n . These a n im a ls
depend l a r g e l y upon th e c i l i a on th e f r e e s u r f a c e of
t h e e p i t h e l i a l c e l l s to c a r r y t h e i r fo o d to th e
sto m ach .
8 . E so p h a g e a l g la n d s a r e found i n each on ly a t th e
p o s t e r i o r end of th e org an and p e n e t r a t e th e subm ucosa.
9. E so p h a g e a l g la n d c e l l s ta k e th e s t a i n a n d a p p e a r l i k e
th e c e l l s o f t h e fu n d ic g la n d s of t h e stom ach. Two
k in d s of c e l l s a r e o b se rv e d i n th e fundus o f t h e s e
g l a n d s ; t h o s e w bich s t a i n l i g h t l y and t h o s e v /h ich tak e
a d a r k s t a i n .
10. T ubules o f e s o p h a g e a l g la n d s e n t e r t h e lumen of th e
o rg a n w here th e e p i t h e l i u m d ip s down b etw een c o n n e c
t i v e t i s s u e p a p i l l a e .
11. The e p i t h e l i u m i s p s e u d o s t r a t i f i e d , a l l th e c e l l s
r e a c h in g th e basem en t membrane.
65
STUmCE
1 . I n each an im al the stom ach e p i t h e l i u m c o n s i s t s of
s im p le colu m nar c e l l s w hich s t a i n d e e p ly n e x t th e
lum en.
2. G a s t r i c g la n d s occur i n the mucosa.
3. T. r a t h b u n i h as th e m ost sim p le g la n d s t r u c t u r e ,
s i n g l e t u b u l e s p r e d o m in a te .
4 . I n a l l t h r e e sp e cim en s g la n d s o f sim p le ty p e a r e more
num erous in th e fundus th a n i n th e p y l o r i c p o r t i o n .
5. Two k in d s o f c e l l s o c c u r i n th e fu n d u s of th e g l a n d s :
c h i e f and p a r i e t a l . C h ie f c e l l s a r e m ost num erous a t
th e b l i n d ends o f th e t u b u l e s . P a r i e t a l c e l l s a r e
j u s t below t h e n e c k of th e g la n d . T here a re more
p a r i e t a l c e l l s i n t h e fu n d u s o f t h e stom ach th a n i n
th e p y l o r i c p o r t i o n .
6 . The change i n c e l l s t r u c t u r e b etw een t h e fu n d u s and
p y l o r i c stom ach i s g r a d u a l .
7. The g la n d ^ s p i t s of A neides a r e l o n g e r t h a n t h o s e o f
th e o t h e r two s p e c im e n s .
8 . The m u s c u la r is m ucosse v a r i e s i n t h i c k n e s s . In
T. r a t h b u n i i t i s t h i c k e r t h a n th e e x t e r n a l m u scle
66
l a y e r of th e fu n d u s and i s c o n tin u o u s a ro u n d t h e
o rg a n . The l o n g i t u d i n a l l a y e r i s t h i c k e r th a n th e
c i r c u l a r l a y e r . The m u s c u la r is mucosa i s alw ays
t h i c k e r i n t h e d o r s a l w a l l . I t i s t h i n n e r i n th e
p y l o r i c p o r t i o n of t h e stom ach t h a n i n t h e fu n d ic
p o r t i o n .
9. The d i g e s t i v e s u r f a c e i s i n c r e a s e d by l a r g e su b
m ucosal f o l d s w ith t h e i r c o v e rin g of m ucosal
g la n d s and e p i t h e l i u m i n _T jL t o r o s u s and ^ l u g u b r i s
l u g u b r i s . I n ^ l u g u b r i s l u g u b r i s f u s i n g o f p l i c a e
o c c u rs betw een a d j a c e n t f o l d s o r t h o s e from opposite
s i d e s . Ro f u s i n g o f p l i c a t i o n s o c c u rs i n T r i t u r o s ,
th e l a r g e s t b e in g i n the d o r s a l w a l l .
10. The e x t e r n a l m uscle l a y e r of t h e stom ach i s t h i c k e r
i n th e d o r s a l w a ll and i n t h e p y l o r i c r e g i o n . In
t h e s e t h r e e sp ecim en s t h e l o n g i t u d i n a l l a y e r i s
alw ays t h i n and som etim es a l t o g e t h e r a b s e n t or i t
o c c u rs i n clum ps w i t h w id e sp a c e s b etw een them.
P e r i s t a l t i c a c t i o n must be weak and d i g e s t i o n slo w .
11. More d i g e s t i o n m ust o ccu r i n th e p y l o r i c p o r t i o n
t h a n i n the fu n d ic p a r t of the stom ach, b e c a u s e
more g a s t r i c g la n d s a r e p r e s e n t i n t h a t p o r t i o n of
th e sto m a c h and th e d i g e s t i v e w a l l i s t h i c k e r .
SMALL INTESTINE
1. The m ucosal e p i t h e l i u m i s s t r a t i f i e d and th e c e l l s
p o s s e s s heavy c ro s s s t r i a t i o n n e a r t h e i r f r e e end.
S. E p i t h e l i a l c e l l s a r e o f two t y p e s : g o b l e t and
co lu m n ar.
3. The w a l l o f th e m a tu re g o b l e t c e l l n e x t th e i n
t e s t i n a l lumen i s t h i n and r u p t u r e s f i n a l l y t o
e x p e l i t s s e c r e t i o n i n t o t h e i n t e s t i n e .
4 . The m u s c u l a r i s mucosae o c c u rs i n T .t o ro s u s and
A. l u g u b r i s l u g u b r i s b u t i s n o t w e l l d e v e lo p e d .
I t o c c u rs i n t h e a n t e r i o r p o r t i o n b u t f a d e s o u t
i n t h e p o s t e r i o r p a r t , and c o n s i s t s a lm o st
e n t i r e l y of c i r c u l a r f i b e r s . The l o n g i t u d i n a l
f i b e r s o c c u r i n s m a ll r e s t r i c t e d a r e a s and a r e
n e v e r c o n tin u o u s a ro u n d t h e o rg a n . O fte n i t i s
a l t o g e t h e r m is s in g i n t h e v e n t r a l w a l l . In
‘ £ jl r& th b u n i t h i s l a y e r i s n o t p r e s e n t .
5. The subm ucosa is a t h i n c o n n e c tiv e t i s s u e l a y e r
i n w hich t h e i n t e s t i n a l lymph g la n d s a r e l o c a t e d .
They a r e s im p le g la n d s and a re m ost numerous i n
t h e a n t e r i o r p o r t i o n of th e i n t e s t i n e .
6 . The subm ucosa i s th ro w n i n t o num erous p l i c a t i o n s .
The duodenum p o s s e s s e s t h i n l e a f - l i k e p l i c a t i o n s
68
w hich a r e c lo s e t o g e t h e r and t e n d to e n c i r c l e th e
o rg a n fo rm in g l a t e r a l and l o n g i t u d i n a l b r a n c h e s w hich
f u s e r e p e a t e d l y . The jejun um p o s s e s s e s t h e t a l l e s t
p l i c a t i o n s w h ile th e ile u m has p l i c a e w hich a re
lo w e r and f a r t h e r a p a r t . These f o l d s g r e a t l y i n
c r e a s e t h e a b s o r p t i v e s u r f a c e . T here i s no a b r u p t
change b e tw e e n t h e d i v i s i o n s o f t h e s m a ll i n t e s t i n e .
7. The m u s c u l a r i s e x t e r n u s c o n s i s t s o f two t h i n l a y e r s
o f f i b e r s . In r a t h b u n i and A. l u g u b r i s l u g u b r i s
t h e l o n g i t u d i n a l f i b e r s a r e r e s t r i c t e d to a few
clum ps i n r e s t r i c t e d a r e a s b u t T. t o r o s u s has a w e l l
d e v e lo p e d l o n g i t u d i n a l l a y e r . The c i r c u l a r l a y e r i s
w e l l d e v e lo p e d b u t v a r i e s in t h i c l m e s s i n a l l t h r e e
s p e c i e s .
LARGE IRTESTIÎTE
1. The m ucosa i s o n ly one c e l l i n t h i c k n e s s .
2. B o th g o b l e t c e l l s and sim p le colum nar e p i t h e l i a l c e l l s
a r e p r e s e n t .
3. The subm ucosa i s n a rro w . No p l i c a t i o n s a r e p r e s e n t
i n t h e p o s t e r i o r p a r t . Lymph g la n d s a r e a b s e n t i n th e
p o s t e r i o r p a r t .
69
The e x t e r n a ] , m u s c l e l a y e r c o n s i s t s a l m o s t e n t i r e l y o f
c i r c u l a r f l o o r s and i s t h i n , o n l y one t o f i v e c e l l s
t h i c k i n p l a c e s . The s e r o s a f o r t h e e n t i r e l e n g t h o f
t h e d i g e s t i v e t r a c t c o n s i s t s of a s i n g l e l a y e r o f
c e l l s .
70
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Creator Barnett, Rena (author)

Core Title Histological variations in the walls of the digestive tract of salamanders

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