Some observations on the nervous system in the strobila of <italic>Monieza expansa</italic>

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Content SOME OBSERVATIONS ON THE NERVOUS SYSTEM
IN THE STROBILA OF MONIEZA EXPANSA
A Thesis
Presented to
the Faculty of the School of Liberal Arts
l&ilversity of Southern California
In Partial Fulfillment
of the Requirements for the Degree
Master of Science - in - Zoology
by
Samuel H. Chain
June 1956
UMI Number: EP67090
All rights reserved
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UMI EP67090
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Research in partial fulfillment of the require
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IVEASTSa OF SCIENCE
'tary
Dean
Date........JjUnj8.ÿ.Xât56.
Faculty Committee
Chairman
TABLE OF CONTENTS
SECTION PAGE
I. INTRODUCTION............................ 1
II. TECHNIQUE AND MATERIAL.......... 3
III. REVIEW OF THE PHTLOGENY OF THE NERVE CELLS
IN INVERTEBRATES...................... 5
IV. NERVOUS SYSTEM IN THE STROBILA OF
CESTODES....................... 9
V. OBSERVATIONS AND DISCUSSION............ 11
VI. CONCLUSIONS ...................... 14
LITERATURE CITED ......... 15
PLATES ........... 18
INTRODUCTION
The selection of the strobile of Monieza expansa as
material for the study of a nervous system of the lower in
vertebrates was made with a definite understanding of the
complicated problems likely to be encountered. The nervous
system of lower invertebrates, according to Parker (*19),
consists of a diffuse net-like arrangement of protoneuronic
nerve cells, with the possibility of the higher inverte
brates approaching the neuronic type of structure. With
this in mind, tapeworms or cestodes in general, might be
expected to show a type of structure somewhere between the
protoneuronic and neuronic types of structure of the nervous
system. This assumption might be true providing the effects
of parasitism have not brought about a degeneration of such
nervous tissue. In addition to this problem, the interpre-
taticHi that the transverse commissure constitutes the ante
rior end of an individual animal of the strobila has been a
vaguely suggested and contested point for many years. (Wat
son *11).
In the beginning it was thought that these experi
ments would aid in the solution of that problem, but a criti
cal analysis of the results of the observations so far indi
cates the need of a tremendous amount of work cytologic ally
and experimentally before conclusions may be drawn to answer
2
that qi&BSti(m.
ConsMéxlng the above factory, it seemed practical to
begin the study of the nervous tissue of cestodes by the use
of differential stains that have been found satisfactory for
the study of vertebrate tissues. For material to stain,
Monieza expanse proved to be the most suitable of the ces-
tode material investigated to date.
TECHNIQUE AND MATERIAL
Sectioning. In the preparation of the tissue for
sectioning, the paraffin method as given in Guyer (*26) and
MeClung (*29) was followed. The paraffin sections were cut
at 10 microns. Both transverse and longitudinal sections
were made.
Stains. For the nervous system the following stains
were used:
1. Methylene blue to show the non-medulated fibers.
2. Gallocyanine (Einarson *32) to bring out the
Nissl bodies and nuclei of the nerve cells.
3. Hematoxylin-eosin and iron-hematoxylin for gen
eral staining of the tapeworm.
Mounting. The sections were mounted in euparal.
Material. Monieza expanse Underhill (’29). The scolex
is small, generally pear-shaped. The suckers are slightly
salient and slit-like. The anterior part of the chain is
filiform. The first segments are very short, those which
follow becoming longer, but always much broader than long.
The broadest segments may reach the breadth of 3/4 of an
inch. The genital pores are double and located on the lat
eral margins of the segments. These tapeworms are found in
the intestinal tract of cattle, sheep, and goats. The length
of the strobila varies considerably; it may be 15 to 30 feet
or more.
The tapeworms were fixed in a special fixing fluid:
Formalin 10 per cent
95^ Alcohol 25 « «
Acetic acid 5 * *
Glycerin 10 ” ”
D. HgO 50 « «
REVIEW OF THE PHÏLOGENY OF THE NERVE CELLS
IN INVERTEBRATES
The nervous systems of Invertebrates have generally
been looked upon as being in principle of different structure
from that of the vertebrates. The union of the nerve cells,
at least in lower invertebrates, is said to be of a contin
uous nature. In the vertebrates the union of nerve cells is
brought about by means of a synapse. If the union of nerve
cells were continuous in the invertebrates, the neurones
would be of a non-polarized type, as distinct from the polar
ized neurones of the vertebrates.
Regarding the continuous or synaptic nature of union
of neurones in invertebrates, Bethe (*05) believed that the
nerve cells of lower invertebrates were united by means of
continuous neurofibrillae, which crossed to two adjoining
nerve fibers.
Parker (*19) in his studies of the nervous systems
of coelenterates has found it to be composed of a nerve net.
Evidence was soon brought together to show that nerve nets
were at least components of the nervous systems of echino-
derms, worms, arthropods, and even vertebrates. Judging
from the fact that the nerve net is apparently the exclusive
type of nervous organization in coelenterates, and that it
becomes less and less evident the higher the animal series
6
is ascended, it seems fair to conclude that the nerve net is
the more primitive type. It is also evident that the nerve
net in the course of evolution has given way more and more
to the synaptic system which has finally come to be the dom
inating plan of nervous organization in the more complex
animals. From this viewpoint one of these animals might
well possess both types of structure, nerve nets having been
retained in its more conservative portions and synaptic
structures having been developed in its more progressive
parts. Thus the nerve net may be regarded phylogenetically
older than the synaptic system. Parker (*18) has used the
term * * protoneurones” to designate the peculiar form of ner
vous structure characteristic of the nerve plexus of lower
invertebrates, i.e., the non-polarized form of nerve cells.
Rogers (*27) lists the following characteristics of
the nerve net:
1. The cells of the nerve net are not only in phys
iological but in structural continuity.
2. The cells of the nerve net are in intimate rela
tions with the muscle cells which they excite.
5. In transmission, impulses flow more freely into
regions where the net is stretched than into regions where
it is not stretched.
4. The nerve net provides for organic autonomy.
7
5. Transmission in the nerve net is diffuse.
6. The power of the nerve net to bring about coordi
nation movements depends upon its refractory phase, i.e., im
pulses brought to bear upon the cells during their period of
activity are not effective in inducing reactions.
7. Evidences of polarity of the nerve net indicate
that the net tends to become converted into a synaptic sys
tem.
8. Modification of the nerve net of such a sort as to
render the fibrils elongated so as to place the nerve cells
at some distance from the muscular cells, and the fibrils
tend to become aggregated in trunks or bands, mark a change
in form from a true nerve net to a synaptic system.
Concerning recent investigation on the structural dif
ferences between the vertebrate and invertebrate nervous sys
tem, Bolzer (*27), in his paper on the nerve cells of coelen
terates, has shown that they are united by means of a synapse.
According to Bolzer the synapse can only be shown in prepara
tions which have not shrunk in the chemical solutions used.
This fact makes it possible to understand the mistake of the
previous authors.
Sanchez (*20), another investigator, has proved through
his work on the origin of nerve cells of invertebrates in in
sects, that the nerve cells of these animals originate in
neuroblasts, similar in form and development to those of ver-
8
tebrates.
Hanstrom ( *28) believes the neurone theory can be ap
plied to the nervous system of invertebrates in the whole ex
tent, and whenever a continuous unicHi between the nerve cells
of invertebrates is to be found, it certainly represents a
secondary phenomenon. From this point of view, there exists
no real difference in this respect in the nervous systems of
invertebrates and vertebrates.
NERVOUS SYSTEM IN STROBILA
OF CESTODES
Regarding the nervous system in the strobila of ces
todes in general, Lankaster (*0l) describes it as containing
one, sometime two, marginal nerve cords, which are, in sev
eral instances at least in the higher forms, united by a
transverse or circular commissure near the hinder margin of
the proglottid. In connection with these longitudinal main
cords is a superficial net work of nerve fibers.
Fantham, Stevens and Theobald (*16) describe the pro
glottid as containing longitudinal fibers which run through
the strobila. The fibers at the lateral borders are usually
the largest.
Kukenthal and Krumbach (*3l) describe the nervous
system in the strobila as consisting of two main longitudi
nal nerves running lateral and external to the excretory
(system) vessels. Running dorsal and ventral to the main
longitudinal cords are the accompanying nerves which are,
according to them, found in all cestodes with the exception
of Monieza Blanchard. (Text Figure l) Outside of these six
lateral strands, one finds constantly two dorsal and two
ventral median longitudinal nerve strands which are contained
between the transverse and longitudinal musculature of the
10
parenchyma. The longitudinal nerves are commonly joined at
the posterior end by a ring or commissure. At the periphery
the nerve fibers of the ring nerves flow in part to the ac
companying nerves, and in part to the main nerves. From the
ring nerves as well as the main nerves, go countless nerves
radially arranged to the periphery which form a fine plexus.
Figure 1
Cestoda - Cyclophyllidea - Monieza expanse (Rudolphi)
Nervous System of the Strobila.
eb - excretory system; din - dorsal longi
tudinal nerve; vln - ventral longitudinal
nerve; gn - genital nerve; hnc - posterior
nerve commissure; Ig - lateral ganglion of
lateral longitudinal nerve; In - lateral
longitudinal nerves; vln - ventral longi
tudinal nerves.
(After Tower)
din vln
hnc
m m m m
Z
/
OBSERVATIONS AND DISCUSSION
After making a series of slides, both longitudinal
and transverse sections, the author foimd that in the
staining of the sections, galacyanine and hematoxylin and
eosin gave the best results for study. In the use of
methylene blue as a nerve fiber stain, the author has had
little or no success. Perhaps the use of methylene blue
supra vitally would have given better results, but this
remains for further experimentation.
After three months of stWy it is the author ^ s
opinion that the morphology of the nervous system in the
strobila of Monieza expansa consists of two main longitu
dinal nerve bands which arise from the so-called central
nervous system located in the scolex of the tapeworm.
These longitudinal nerve bands are located in the medullary
layer of the proglottid and run through the length of the
strobila. At the posterior border of the proglottid, the
longitudinal nerve bands are joined by a commissure. Con
nected to the longitudinal nerve bands, and running through
out the cortical layer of the proglottid, lie the dorsal
and ventral nerve nets of the strobila.
The longitudinal nerve bands and nerve nets are made
up of darkly staining nerve cells which are in structural
12
continuity by means of fibers arising from their cell
bodies. These darkly staining cells and their fibers send
out processes which Innervate the important organs and
tissues of the strobila.
From the above observations it is the opinion of
the author that the nervous system represents a higher modi
fication of the primitive nerve net systems of the lower
invertebrates. From the study of the dorsal and ventral
nerve nets, it is quite reasonable to relate the nerve
cells of the net to those of the protoneuronic type in the
lower invertebrates. This is possible by comparison of
their unipolar form and structural continuity. Another
structure possessed by the nerve net that is characteristic
of nerve nets of lower invertebrates is the diffuseness of
the cell bodies and their processes throughout the cortical
layer of the strobila.
Regarding the longitudinal nerve bands of the stro
bila, the author is of the belief that they have been dif
ferentiated from the dorsal and ventral nerve nets. The
reason for this viewpoint is that of structural similarity
of the non-polarized nerve cells of both the dorsal and
ventral nerve nets and the longitudinal cord. It can be
reasonably admitted that the formation of the longitudinal
nerve band and its connection with the so-called brain of
the scolex is a step forward in the evolutionary scale of
13
nervous development.
Before ending the discussion, the author wishes to
state that a great deal of work must he done regarding the
comparative effect of nerve stains upon the nerve cells of
vertebrates and invertebrates. In the present study the use
of galacyanine did not bring out the Nissl substance of the
nerve cell, for which purpose it is commonly used.
CONCLUSIONS
1. The strobila nervous system of Monieza expanse
is of a higher type of development than that of the nerve
nets of the lower invertebrates.
E, The nerve cell structures are very much like
the protoneuronic nerve cells of lower invertebrates.
LITERATURE CITED
Bethe, A.
1903. Allgemeine Anatomie und Physiologie des
Nervensystem. Leipzig.
Bolzer, H.
1927. Untersuchimgen uber das Nervensystem der
Coelenterates. Zeitschrift f. Vergl. Phys.,
Bd. 6.
Einarson, L.
1932. A Method for Progressive Selective Staining of
Nissl and Nuclear Substance in Nerve Cells.
Amer. Jour. Path., Vol. VIII, pp. 295-307.
Fantham, H.B., Stevens, J.W.W., Theobald, F.V.
1916. The Animal Parasites of Man. John Bale, Sons
and Danielson Ltd., London.
Guyer, M.F.
1926. Animal Micrology. University of Chicago Press,
Chicago.
Hanstrom, B.
1928. Some Points on the Phylogeny of Nerve Cells
and of the Central Nervous System of Inverte
brates. Jour. Comp. Neurol., Vol. XLVI, p.
475.
Kukenthal, W., Krumbach, T.
1931. Handbuch der Zoologie. Zweiter Band. Walter
de Gruyter and Co. Leipzig.
Lankaster, C.A.
1901. A Treatise on Zoology. Part IV, Platyhelmia,
Metazoa and Nemertina. Adam and Charles
Black. London.
Me Clung, C.E.
1929. Handbook of Microscopical Technique. Paul B.
Hoeber. New York.
Parker, G.H.
1918. Some Underlying Principles in the Structure of
the Nervous System. Science, n.s. Vol. XLVI I.
16
1919. The Elementary Nervous System. Lea and
Febiger. Philadelphia.
Rogers, C.G.
1927. Textbook of Comi^rative Physiology. McGraw-
Hill Book Company, Inc. New York.
Sanchez, R.
1920. Sobre el Desarollo de los Element os Nerviosos
en la Retina del Pier sis brassiceae. Trab.
d. Lab. d. Investig. Biol. d. 1. Ikiiv. d.
Madrid. Madrid, Spain.
Watson, E.E.
1911. The Genus Gyrocotyle. University of Califor
nia Publications in Zoology. Berkeley Press.
PLATES
PLATE I
Longitudinal section through the proglottid
(x850)
Inc - longitudinal nerve cord; Im - longitu
dinal muscles; pc - parenchymal cells; c -
cuticle; u - uterus.
H
Si~âî4
PL f r r £ = ^ z
PLATE II
Longitudinal section of proglottid showing
longitudinal nerve band cells and
their processes. (xl270)
%
2 r
PLATE III
Cross section of proglottid showing nerve
net of the cortical layer. (x250)
nn - nerve net cells; c - cuticle; p -
parenchymal cells.
f
f^lSTt: JZt
PLATE IV
Cross section of proglottid showing nerve
net and transverse muscle fibers.
(xl270)
JuT
PLATE V
Longitudinal section of proglottid showing
Icmgltudlnal nerve band, processes in
nervating genital system and longitudi
nal musculature of strobila. (xl270)
Inb - longitudinal nerve band; u - uterus;
Im - longitudinal muscles.
c
»
w
pijfTË %:

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Creator Chain, S. H. (author)

Core Title Some observations on the nervous system in the strobila of Monieza expansa

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Degree Master of Science

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