Memoirs from the Biological Laboratory
OF THE
JOHNS HOPKINS UNIVERSITY
IV, 4
WILLIAM K. BROOKS, EDITOR
PHYSIOLOGY AND HISTOLOGY
OF
THE CUBOMEDUSÆ
INCLUDING
DR. F. S. CONANT’S NOTES ON THE PHYSIOLOGY
A DISSERTATION PRESENTED TO THE BOARD OF UNIVERSITY STUDIES
OF THE JOHNS HOPKINS UNIVERSITY
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
BY
E. W. BERGER
BALTIMORE
THE JOHNS HOPKINS PRESS
1900
[Illustration]
PRINTED BY
The Lord Baltimore Press
THE FRIEDENWALD COMPANY
BALTIMORE, MD., U.S.A.
This Memoir is a continuation of the work upon the Cubomedusæ which was
begun by the late Dr. FRANKLIN STORY CONANT, and it contains his notes
of physiological experiments, as well as new results which have been
obtained by Dr. E. W. BERGER from the study of material which had been
collected by Dr. CONANT, who had hoped to make it the object of further
study.
In order that this work may be made public as a continuation of Dr.
CONANT’S researches, his sister, GRACE WILBUR CONANT, has, with the
coöperation of other members of his family, made an adequate and generous
provision for its publication.
For this gift, which is at once a contribution to science and a memorial
of an able and promising investigator, lately student and fellow in
this institution, the Johns Hopkins University returns its grateful
acknowledgments.
DANIEL C. GILMAN, _President_.
W. K. BROOKS, _Professor of Zoölogy_.
CONTENTS.
PAGE
INTRODUCTION.
History 1
Epitome of Anatomy 2
PHYSIOLOGICAL.
CHARYBDEA.
Light and Darkness 5
Concretions 8
Sensory Clubs 9
Velarium and Frenula 11
Pedalia, Interradial Ganglia, Tentacles 12
Stomach, Suspensoria, Proboscis, Subumbrella 13
Margin, Radial Ganglia, Nerve 15
Stimulation 17
Activity of Charybdea 17
Temperature 17
Food and Feeding 18
Occurrence of Charybdea 18
AURELIA AND POLYCLONIA (_Cassiopœa_) 19
SUMMARY 22
DR. CONANT’S NOTES.
CHARYBDEA.
Light and Darkness 24
Sensory Clubs 26
Nerve 29
Side, Subumbrella 30
Pedalia, Velarium, Ganglia 31
Tentacles 32
Proboscis, Stomach, Phacelli 33
Temperature 33
Food and Feeding 33
Occurrence of Charybdea 33
Activity of Charybdea 34
AURELIA AND POLYCLONIA 35
CASSIOPŒA 39
AURELIA 39
HISTOLOGICAL.
Method 40
Anatomy 41
Distal Complex Eye--
General 41
Cornea 42
The Lens 42
The Capsule 44
The Retina 45
(a) The Prism Cells 46
(b) The Pyramid Cells 48
(c) The Long Pigment Cells 50
(d) Subretinal Nerve Tissue 53
(e) Discussion of Literature 53
(f) Function of the Retinal Cells, Patten’s Theory, and
further Literature 56
The Proximal Complex Eye 60
The Simple Eyes 61
Lithocyst and Concretion 63
The Epithelium of the Clubs 64
Network and Multipolar Ganglion Cells 67
The Nerve Tissue 67
The Supporting Lamella 68
Epithelium of Ampulla and Floating Cells 68
The Endothelium of the Peduncle 73
The Tentacles and Pedalia--
The Ectoderm 74
(a) Thread Cells 74
(b) Muscle Fibers 74
(c) Ganglion Cell 75
The Endoderm 75
SUMMARY 77
LITERATURE 78
REFERENCE LETTERS 80
DESCRIPTION OF FIGURES 81
INTRODUCTION.
This paper may be regarded as a continuation of the Cubomedusan studies
pursued by Dr. F. S. Conant while in Jamaica, in 1896 and 1897, with the
Johns Hopkins Marine Laboratory. His systematic and anatomical results
have since been published as his Dissertation (“The Cubomedusæ”) by this
University. Conant described this paper as Part I, hoping soon to add
a second part on the physiology and the embryology, for which he had
some notes and material at hand. Returning, however, to Jamaica with the
laboratory, in 1897, he continued his physiological experiments, and
preserved material for histological purposes. Upon the untimely death
of Conant, his material and notes were placed in my hands by Professor
Brooks, to whom I here take the opportunity of expressing my appreciation
and sincere thanks for the honor thus conferred and for the many favors
received.
In this paper I shall note at some length Conant’s physiological results
and append his notes. I shall also add my results on the histology of
the eyes and the sensory clubs in general, with some few facts on the
histology of the tentacles. The embryology will be reserved for a future
paper.
The forms used in the physiological experiments were Charybdea Xaymacana,
one of the two species (see Literature V, a and b) first found and
described by Conant; Aurelia aurita; Polyclonia and Cassiopœa. The
greater number of Conant’s notes are on Charybdea, and were left by him
just as taken at the time of experimenting. Many of these notes are
highly interesting and in the main fit in well with Romanes’[I] and
Eimer’s[IV] results.
Dr. Conant’s work on Charybdea, in 1897, was wholly done at Port Antonio,
Jamaica. At first Conant had only varying success in obtaining Charybdea,
scouring the harbor and neighboring water at all hours, only to obtain
but few specimens. It was on the forenoon of August 7th, while we were
dredging at the head of East Harbor with a steam launch, that many
Charybdeæ were brought up in the dredge. This gave Conant a clue to
their whereabouts and to the means of obtaining them, and from that time
on he was able to obtain them in abundance. His first physiological
experiments were begun on August 4th and continued thereafter at
intervals of several days until his departure from Jamaica on September
6th.
Dr. Conant usually performed his experiments during the second half
of the forenoon, after the animals had stood for a few hours in the
laboratory.
The building that was rented at Port Antonio for a laboratory had, in
the basement, a photographer’s dark-room, which was of great service to
Conant in his experiments.
The experiments on Aurelia, in 1897, were also performed at Port Antonio,
between August 6th and 9th. The experiments on Cassiopœa were probably
made at Port Antonio, where specimens were occasionally obtained.
The notes on Aurelia and Polyclonia, in 1896, were taken at Port
Henderson, between May 12th and June 27th.
In his notes Conant speaks of Polyclonia and Cassiopœa. It is at present
undetermined whether he really had both forms or whether he uses the two
names for the same form. It seems likely that in 1896 he thought the
form to be Polyclonia, while for some reason, in 1897, he supposed it to
be Cassiopœa. I have examined several specimens of these medusæ brought
from Port Antonio and find that they all have twelve marginal bodies and
twenty-four radial canals, according to which (V, Haeckel’s System),
they should be Polyclonia. Conant, however, speaks of removing sixteen
marginal bodies, which seems to indicate that he had Cassiopœa. A careful
classification of this form of medusæ found about Jamaica seems to be a
desideratum. I suppose, however, that for our purpose in this paper it
will make little difference which name is used, the two forms being so
similar in form and structure. I have, therefore, decided to retain both
the names used by Conant.
For the complete anatomy of Charybdea the reader is referred to Dr.
Conant’s dissertation, “The Cubomedusæ” (8b), or the _Johns Hopkins
University Circulars_ (8a), both published by the Johns Hopkins Press.
But, for the convenience of those who may be less familiar with
Cubomedusan anatomy, the following brief summary of the anatomy of
Charybdea is given:
The Cubomedusæ, as the name implies, approximate cubes, with their
tentacles (four in Charybdea) arranged at the four corners of the lower
face of the cube. These tentacles are said to lie in the interradii.
Half way between any two points of attachment of the pedalia (the basal
portions of the tentacles) and a little above the margin of the bell
(cube), in a niche, hang the sensory clubs, one on each side, four in
all. Each sensory club hangs in a niche of the exumbrella and is attached
by a small peduncle whose axial canal is in connection with one of
the four stomach-pockets and in the club proper forms an ampulla-like
enlargement.
Each club is said to lie in a perradius, and, like the tentacles, belongs
to the subumbrella. This is shown by the course of the vascular lamellæ,
bands of cells that, stretching through the jelly from the endoderm to
the ectoderm all around the margin, form the line of division between
sub- and exumbrella.
Each club has six eyes. Two of these on the middle line of the club
facing inwards are called the proximal and distal complex eyes, to
distinguish them from the four simple eyes that are disposed laterally,
two on each side of the line of the two complex eyes. All of these eyes
look inwards into the bell cavity through a thin transparent membrane
of the subumbrella. Besides the eyes and the ampulla already mentioned,
a concretion fills the lowermost part of the club, and a group of large
cells, having a network-like structure and called network cells by
Conant, fill the uppermost part of the club between the proximal complex
eye and the attachment of the club to its peduncle (Plate II, Fig. 13).
What is evidently nerve tissue, fibers and ganglion cells, fills the rest
of the club, with two groups of large ganglion cells disposed laterally
from the network cells. A sensory (flagellate) epithelium covers the club.
Most Cubomedusæ, among them Charybdea, have a velarium (comparable to the
velum of the Hydromedusæ), a membrane of tissue that extends inwards at
right angles all around the margin. This velarium, like a velum, has a
central opening through which the water is expelled from the bell-cavity
when the animal pulsates. In the perradii and in the angle between the
velarium and the body wall, are the frenula, which give support to
the velarium much like brackets support a shelf, except that here the
brackets are above the shelf instead of below.
In the upper part of the bell is the stomach, with the phacelli in its
interradii, and continued ventrally into the manubrium, or the proboscis.
The cavity of the stomach is continued in the perradii through the four
gastric ostia into the four stomach pockets, which occupy the sides of
the bell and extend to the margin. Immediately below the gastric ostia,
and in the bell cavity, are the suspensoria, one in each perradius.
These support the floor of the stomach much as the frenula support the
velarium, except that the suspensoria are placed under the shelf (to
continue Conant’s figure) and not above it as are the frenula.
A nerve ring, underneath the epithelium of the subumbrella, passes from
near the origin of each pedalium at the margin to the origin of the
peduncles of the sensory clubs, a little above the margin, giving off a
branch to each club. Eight ganglia are found in the course of this nerve.
The four pedal ganglia lie near the bases of the pedalia, and are hence
interradial; the four radial ganglia lie near the bases of the peduncles
of the clubs, and are perradial. A small nerve, radial nerve, can be
traced a short distance upwards from each radial ganglion. Underlying
the epithelium of the frenula and the suspensoria are ganglion cells and
nerve fibers in larger numbers than elsewhere (excepting the ganglia
mentioned) in the subumbrella. Otherwise, ganglion cells and nerve fibers
underlie the epithelium of the subumbrella, including the inner surface
of the velarium, as also do muscle fibers, except in the perradii and in
the region of the nerve, where the latter become interrupted.
PHYSIOLOGICAL.
CHARYBDEA.
_Light and Darkness_--Experiments 1-9, 10, 33, 34.--As already stated
in the Introduction, a part of Conant’s experiments were performed
in a photographer’s dark-room, with the animals in a deep glass jar.
In the dark a fair proportion of the animals became nearly quiescent
on the bottom, but upon lighting a lamp many started up immediately,
while others took a longer time to come to the surface and swim. These
experiments were tried a number of times and on different occasions with
very similar results. Some medusæ, however, tried immediately after
being brought in, seemed not to react so well upon being placed in the
dark-room, nor would they become quiescent. This, probably, was due to
the fact that the animals had not yet recovered from the effects of being
caught and placed in new surroundings. (Experiments 1, 2, 3.)
Other experiments (4-8, 33, 34) were tried by carrying the jar with the
animals from the weaker light of a room into the more intense light of
outdoors or into direct sunlight. The usual result was an inhibition of
pulsation and a settling to the bottom, while the medusæ immediately
became active again upon returning with them to the room. These results
were so marked that no doubts can be entertained as to their cause,
though some exceptions occurred in which animals placed in the sun
continued to swim on the surface or soon recovered pulsation. In some
experiments, too, no animals responded to the inhibitory stimulus of the
brighter light or all very soon recovered. (See, however, Temperature.)
Reducing the light by placing a coat over the jar produced the same
effect in some experiments (8, 9, 10) as did reducing the light in other
ways, while removing the coat produced the same effect as exposure to
brighter light. In these instances it appears to be the transition from
weaker to stronger light that inhibits pulsation, rather than the actual
intensity of the light; and _vice versa_. It must be noted, too, that
when left for some time in any one place the animals changed, some
coming to the surface and others going to the bottom.
These experiments show beyond doubt that Charybdea is sensitive to
light, and that it is moderate light that stimulates the animals to
activity, while darkness and strong light inhibit activity. While the
individual exceptions, as Conant himself suggests, are well explained
on the supposition of individual diversity, yet it appears that other
conditions, such as the time of day, temperature, etc., may have been
responsible for some of the exceptional experiments in which no animals
responded as expected.
While light of any intensity seems to have stimulated Romanes’[I] Sarsia
and Tiaropsis (Hydromedusæ) to activity, we note that it is moderate
light that stimulates Charybdea. This fact is evidently correlated with
the circumstance that Charybdea usually lives upon or near the bottom.
It may further be added in regard to Romanes’ Tiaropsis polydiademata,
that when it was suddenly exposed to light it went into a spasm
preceded by a long latent period during which there was a “summation of
stimulating influence” in the ganglia. Sarsiæ would congregate toward
the source of light and in general were more active in light than in the
dark, while sudden darkness often inhibited a swimming bout. Romanes
proves for Sarsia that the marginal bodies are the seat of luminous
stimulation and that it is the light rays and not heat rays that
stimulate. He also remarks that he has obtained similar results on the
covered-eyed (Scyphomedusæ) medusæ, namely, that they respond to luminous
stimulation.
It may here be of interest to note a few observations made by myself at
Wood’s Holl, Mass., on a beautiful Olindiad, which is abundant in the
Eelpond at the above place. I found that in a room, in the ordinary light
of evening, the animals swam actively; but the moment the electric light
was turned on they stopped swimming and settled to the bottom or attached
themselves to a branch of some weed or stem suspended in the water.
This was the result in every trial. It is found, further, to be little
active during the brighter parts of the day, when one must dip quite deep
with a net in order to obtain it. A similar observation is also made by
Murbach[II], who further states that this medusa may be deceived into
laying its eggs by placing it in the dark.
One cannot help but remark how analogous is the behavior of medusæ, in
respect to light and darkness, to the behavior of many of the higher
animals,--and medusæ are among the most lowly organized of the animal
creation.
Were one to conclude from the behavior of Charybdea in light and darkness
in the laboratory, that it remained on or near the bottom in the daytime
but became more active near or at the surface evenings, nights and early
mornings, one would probably not be far from the truth. Dr. Conant,
while towing near the bottom with a weighted net, in water four to five
feet (1.2-1.5 m.) deep not far from shore and deeper farther out, found
Charybdea in abundance mornings and afternoons, but very few in the
evening. In the evening some few were usually taken in the surface tow.
(See Introduction, Occurrence and Activity.)
Again, who knows but that Charybdea is active during the day, on the
bottom where it was dredged (the light there would only be moderate),
and quiet at night. This supposition would seem to be true, at least,
for those forms of Cubomedusæ that live in deep water. We can hardly
suppose that they should regularly rise to the surface from great depths
and become active. This much we do know that bright light inhibits
Charybdea’s activities, while it probably would not be active in perfect
darkness.
I do not know just what interpretation to put upon Conant’s finding
Charybdea at Port Henderson at the surface during the early part of the
forenoon, before the sea-breeze roughened the water (“Cubomedusæ” p. 7).
This fact hardly fits in with my conclusions above. Perhaps Charybdea’s
habits vary with its habitat.
Finally, while I find no experimental evidence in Conant’s notes about
what parts of Charybdea are sensitive to light, yet it would seem
preposterous, from histological evidence and from Romanes’ results on
Sarsia, to doubt that the eyes of the marginal bodies are the seat of
this stimulation.
Dr. Conant further experimented by cutting off certain organs and parts
from the Cubomedusan bell. These excisions consisted chiefly in cutting
out the concretions of the sensory clubs, cutting off the whole club,
eliminating a part or whole of the margin and the velarium, cutting the
bell into sectors, excising the stomach and parts connected with it, and
other parts.
_Concretions_--Experiments 10, 11.--The four concretions were removed
from each of four animals. Two of these (Experiments 10, and another (X),
not appended, to save space) seemed to be little if at all affected by
the operation. One of the two (10) swam actively, at first up and down
more changeably than those intact, but later mostly near the surface.
The other one also swam actively and showed nothing to indicate weakened
sense-perception. The other two (11) did not stand the operation well, as
Conant remarks, and immediately went to the bottom, where they remained,
one swimming, while eight hours later one was still in good condition.
Several attempts with stronger light by removing the coat from the
jar made no difference in the behavior of 10; it continued to swim as
heretofore. Upon a final trial, however, with removing the coat, it went
to the bottom, thus showing a possible reaction to light; but when next
seen it was keeping to the bottom.
That the concretions should function as organs of light sensation, as
the first of the above animals might seem to indicate, I believe is out
of the question.[a] The fact, too, that this same animal (10), together
with another (X), swam actively, immediately changing their course upon
coming to the surface, in reality behaving quite as normal animals,
hardly permits us to conclude from the behavior of the other two (11)
that the concretions function directly as organs of equilibrium or space
relations. May these concretions not function simply as weights for
keeping the sensory clubs with their eyes properly suspended? Since these
concretions lie at the lowermost part of the clubs and in closed sacs and
unsupported by cilia, it would seem that the above suggestion as to their
being weights is not improbable. Direct observation (Experiment 20) by
Conant shows, furthermore, that the clubs always hang with a tendency for
the concretions to be lowermost, regardless of the position of the animal.
Again, while they may function as weights, as just explained, the fact
that the epithelium of the clubs is flagellated (a flagellum, continued
as a nerve fiber, to each cell--see Histology), the supposition lies
near that these flagella are the ones influenced by the concretions as
the clubs bear against one side of the sensory niche or the other. A
somewhat similar view seems to be held by other observers and is noted by
Lang in his text-book (“The outer epithelium of the auditory body carries
the auditory hairs”). It seems, then, that in functioning as weights for
suspending the clubs, they may also serve at the same time for making the
pressure of the club against the niche greater than if they were absent,
and thus in part serve in equilibrium. On this supposition we should
expect, furthermore, that after the removal of the concretions the animal
would be little, if at all, affected, since the clubs themselves, without
the concretions, would still be of sufficient weight to be influenced
by gravity and thus to bear against the walls of the sensory niche. It
must be noted, however, that Conant’s experiments upon equilibration in
Charybdea are negative. Also, that Charybdea has any auditory sense is
negatived by two attempts of Conant’s with a violin--one attempt with the
violin near the animals, and another with it in contact with the dish.
(From an unpublished note.) Hence, some other word such as sensory or
equilibrating should perhaps be substituted for “auditory” in the above
quotation.
Removing the concretions from Aurelia gave negative results very similar
to those on Charybdea. (Experiment 42.)
_Sensory Clubs_--Experiments 12-19, 20, 24.--The entire sensory clubs
were removed from a number of animals. A paralysis of pulsation followed
by a rapid recovery was the usual result. In some instances, however,
there was no paralysis, while in others no recovery followed paralysis.
This is true in a general way whether one club only or all were removed.
While no permanent paralysis followed the removal of one or two clubs,
yet permanent paralysis did occur after the removal of a third club, as,
of course, also after the removal of a fourth. It is evident, too, that
as the removal of the clubs progressed recovery seemed to be weaker after
each cutting, except in one case when pulsation seemed to be quickened
after the removal of a second club. The pulsations after recovery seemed
to be not so strong and regular, often quite feeble, and in one instance
in groups. Pieces of tissue with a club attached and pulsating regularly,
ceased pulsating after removal of the club, in one instance, however,
still giving occasional contractions.
These results are quite the same as those of Romanes[I] on Aurelia,
Cyanæa, etc., and of Eimer[IV] on Aurelia, Rhizostoma, Cotylorhyza,
etc.[b] In these forms Romanes sometimes obtained complete paralysis
after the removal of the sensory clubs only, as also after the removal of
the whole margin, though this was not marked in Aurelia. In Cyanæa and
other forms motor centers seemed to be more abundant than in Aurelia,
so that paralysis was oftener followed by recovery. He concludes that
while the principal motor centers reside in the lithocysts, other centers
doubtless exist that may function vicariously, but that the centers of
the margin are more definitely limited to the marginal bodies in the
Scyphomedusæ than in the Hydromedusæ, in which the whole margin seems
to be replete with centers. He feels positive, furthermore, that no
motor centers exist in Aurelia’s margin outside of the marginal bodies
(lithocysts). Eimer’s results are essentially the same as Romanes’, so
that for a more detailed comparison of the two, Romanes’ works should be
consulted.
Romanes’ conclusion for the Hydromedusæ is that the motor centers are
not so definitely localized in the marginal bodies, but in the margin
generally, the excision of the marginal bodies alone producing only
partial paralysis, as would also the removal of the margin from between
the marginal bodies, but not so marked. For the Hydromedusæ he concludes,
then, that all the centers of spontaneity are definitely localized in
the margin, but not limited to the marginal bodies. To this he mentions
one exception, namely, _Staurophora laciniata_, in which another center
is found near the margin and two others in two opposite arms of the
proboscis.
I made the remark in an abstract (VI) on Conant’s notes that Romanes did
not obtain recovery of pulsation after removal of all the lithocysts in
Aurelia. As noted above, he did obtain recovery, so that Conant’s results
on Charybdea and also Aurelia (see Polyclonia and Aurelia) are quite in
agreement with Romanes.
The paralysis following the removal of the clubs in Charybdea is
evidently, primarily, the result of a loss of a part of its nervous
mechanism (motor centers), and, secondarily, of nervous shock, and
points to the existence of a definite nervous mechanism in the clubs.
The histological evidence is here, as usual, corroborative of the
physiological.
Another interesting phenomenon observed after the removal of one or
all of the clubs was the strange behavior of the proboscis. This would
reach from side to side, expanding and contracting its lips as if
trying to grasp something. This behavior is very similar to that of the
proboscis of _Tiaropsis indicans_ when Romanes stimulated any part of its
subumbrella, or of _Limnocodium sorbii_, a little fresh-water medusa,
when he stimulated its margin or the region of the radial canals. (Ib.,
p. 242.)
I may add that I observed a very similar movement of the proboscis of the
Olindiad, before mentioned. When I pulled off pieces of its gonads by
means of quick jerks, with a small forceps, it would continually reach
toward the injured part of its subumbrella. This medusa is generally
quite active with its proboscis and can occasionally be seen to reach
with it.
Romanes states in one place that the proboscis is not affected by the
excision of the margin. This is evidently not the case in Charybdea,
in which excision of the sensory clubs (which really belong to the
margin--see “Cubomedusæ”) decidedly stimulated the proboscis to active
movements. This, furthermore, points to the marginal bodies as being
organs of considerable importance in giving information in the life of
Charybdea. In Romanes’ Sarsia and other medusæ, however, the proboscis
did respond to the stimulation of the tentacles and the marginal bodies,
as also would the bell respond to a stimulation of the proboscis
(manubrium), thus showing a reflex nervous connection between these
regions of the bell, similar to that described for Charybdea.
_Velarium and Frenula_--Experiments 18, 29, 30, 41c.--“The power of
originating contractions” to use Conant’s own words, “evidently resides
in the velarium or in ganglion cells of the frenula, just as it does
in the proboscis and the floor of the stomach.” Isolated pieces of the
velarium contracted by themselves as did the whole velarium when all
other tissue had been removed. An isolated velarium with the margin and
the pedalia attached gave irregular contractions. When the pedalia with
the _interradial ganglia_ were removed it still contracted; and when all
the other tissue was cut off contractions continued.
Cutting the velarium caused the _pedalia_ to be strongly contracted
inwards so that the tentacles were brought inside the bell. Cutting away
the velarium did not interfere with the pulsations of the bell, but
progress was much retarded.
Cutting the frenula caused the pedalia to contract but seemed not to
affect the ability to swim. Comparing the velarium of the Cubomedusæ
with the velum of the Hydromedusæ, I recall no observations similar
to the ones here noted, though it seems that the two may have quite
similar functions. It seems somewhat probable that the velum, and also
the velarium, may function in obtaining food,--and this besides their
function in swimming. Their probable function in swimming, as is well
known, is evidently to narrow the mouth of the bell and thus to cause
the water to be forced out in a smaller but more rapid stream, giving
the animal a steady and more prolonged movement through the water at
every contraction of the bell. In regard to taking food, I observed that
a small crustacean, in the process of being swallowed by an Olindiad,
seemed to be held by the velum being firmly contracted about it while
the proboscis was working itself over the crustacean. It would seem,
furthermore, that my supposition is supported for Charybdea by the fact
that the pedalia and tentacles were contracted so as to be brought inside
the bell when the velarium was cut. The stimulus of cutting the velarium
may be comparable to a stimulus from some object touching it, and thus
cause the pedalia and tentacles to come reflexly to aid in capturing or
holding the object, a fish, crustacean, or such, to be captured.
_Pedalia, Interradial Ganglia, Tentacles_--Experiments 15, 23, 27-31,
41b.--When the pedalia were removed, the power of the animal to guide
itself was completely gone. When one pedalium was cut the others
contracted, while stroking the outer edge of the pedalia, touching the
sensory clubs, or sharply pricking the subumbrella, often produced the
same result. (See also Nerve.) The upper part of the subumbrella seemed
not so sensitive and more seldom produced the reflex of the pedalia,
while the base of the stomach did not give it at all. Stroking the outer
edge of the pedalia of _Tripedalia cystophora_, the second of the two
species of Cubomedusæ described by Conant, also caused the pedalia to
be contracted inwards. I may note here that the muscle fibers under the
ectoderm of the pedalia are specially well developed at and near the
inner and outer edges, both in Charybdea and Tripedalia. On the flattened
sides of the pedalia the muscle fibers are fewer.
When the pedalia were cut off far enough up to remove the interradial
ganglia, coördination was not affected and the animal could pulsate well
enough but with little progress. (See above under Velarium and Frenula.)
An isolated tentacle is capable of squirming contractions, and when
stimulated at either end, it would contract wholly or in part only.
The pedalia, then, it would seem, serve also as a steering apparatus, for
which they are admirably fitted, considering their blade-like thinness.
Considering, now, the reflexes noted under this head and the preceding
one, we find that there is an intimate nervous connection between the
velarium and frenula, subumbrella, sensory clubs, nerve, and a single
pedalium, on the one hand, and the pedalia on the other hand. This
is born out fully, furthermore, by the histological evidence--(See
Introduction and “Cubomedusæ”). Considering the subumbral plexus of
ganglion cells and fibers, including the velarium and the frenula, which
is in connection with the nerve ring and this again with the sensory
clubs and the interradial ganglia at the bases of the pedalia, we have
a basis for these reflexes. While Conant failed to demonstrate nerves
(“Cubomedusæ”) from the interradial ganglia to the pedalia, yet, that a
nervous connection exists between the pedalia and the bell is well shown
by his physiological experiments. I have, furthermore, demonstrated
ganglion cells under the ectoderm of the tentacles (see Histology).
Romanes obtained quite similar results in the Hydromedusæ. He found
that when a tentacle of Sarsia was slightly stimulated, it alone would
contract, but when it was more strongly stimulated the other tentacles
also would respond as also the manubrium. I find no evidence in Conant’s
notes of any such response of the manubrium of Charybdea, except when the
clubs were cut off.
The reflex obtained on stimulating the subumbrella of Charybdea, when
the pedalia would contract, is somewhat different from that obtained by
Romanes, who found that the most sensitive part of the subumbrella in
producing a reflex of the margin was at the junction of the manubrium
to the bell and that the subumbrella below this point did not give the
reflex.
_Stomach, Suspensoria, Proboscis, Subumbrella_--Experiments 12, 18, 19,
24-26, 29, 31.--The proboscis and the stomach with the phacelli when cut
out, contracted with or without the lips removed. The isolated lips also
contracted (twitched).
Pieces of the sides connected only with the stomach and suspensoria, or
with the margin (Experiment 47 (?)) twitched spontaneously, but seldom
did so when these were removed. In one instance the whole side was cut
out so as to exclude the radial ganglion but still connected with a
portion of the suspensorium. This pulsated, or contracted, but on being
halved transversely, the lower half ceased to contract while the upper
half connected with the suspensorium, continued to contract.
Cutting off the whole stomach end of the animal excited to very rapid
pulsations of the remaining part, with the stream of water stronger out
the aboral end than past the velarium.
Conant says, “It seems I get no good evidence of the subumbrella without
connection with special nerve centers being able to contract by itself.”
The piece in which he did get contractions he suspects may have been
intimately associated with some part of the frenula or the suspensoria.
In Polyclonia no such doubt exists, for small pieces of subumbrella
were seen to contract. A small piece of subumbrella of Charybdea with a
sensory club attached could contract by itself.
From the above it would seem that a center capable of inciting to
contractions resided in the suspensoria as well as in the sensory
clubs, and this may be one of the centers that becomes potent upon the
removal of the clubs. This is further supported by Conant’s observation
(Introduction and “Cubomedusæ”) that an extra large number of ganglion
cells is found under the epithelium of the suspensoria. A somewhat
similarly located center of spontaneity described by Romanes for
_Staurophora laciniata_ (Hydromedusa) has already been noted.
As to the rapid pulsations of the bell after cutting out the stomach
end, this also is similar to Romanes’ results on Aurelia and other
Scyphomedusæ, when he cut off parts of the manubrium or an aboral ring
out of the bell. In these instances, however, Romanes soon obtained
a slackening of the rhythm following the temporary acceleration. The
temporary acceleration he attributes to the stimulus of cutting, and the
slackening to a lack of some afferent stimulus from the removed tissue.
Conant obtained the same results on Polyclonia by removing the oral arms
(see Polyclonia) but says nothing about a slackening of the rhythm in
Charybdea. I believe the increased rhythm in Charybdea was in part due to
the decreased amount of labor necessary to force the water out of two
openings instead of one, namely, past the velarium. Just how much this
observation bears upon Romanes’ theory of rhythmic contraction, that the
rhythm is due to an alternate exhaustion and recovery of the contractile
tissue, as opposed to the ganglionic theory of rhythm of physiologists,
one does not wish to speculate much. Yet, I feel that the observation
rather supports this theory. The tissue having to do less work, would
become less exhausted at each contraction and require less time for
recovery and hence have a more rapid rhythm.
I here sum up Romanes’ theory in a few words. The ganglia liberate a
constant and comparatively weak stimulus, one perhaps about minimal. This
stimulus sets off the contractile tissue; but as the tissue contracts
and becomes exhausted the constant stimulus becomes, in relation to it,
sub-minimal, and it does not contract again until it has recovered and
the stimulus is again strong enough to set it off. The ganglionic theory
of rhythmic contraction supposes that the ganglia liberate stimuli to
the contractile tissue at successive intervals. Romanes had this theory
suggested to him by the rhythmic contractions he succeeded in obtaining
by subjecting deganglionated bells to a continuous but weak faradic
stimulus, or by placing them into weakly acidulated water, or into 5 per
cent. glycerine. Romanes claims that his theory better explains muscular
tonus and the contraction of involuntary muscle. He does not, however,
hold this theory to the exclusion of the ganglionic theory, since only
too often does he speak in terms of the latter. He further brings in his
support the fact that the frog’s tongue, in which no ganglia have been
demonstrated, can be made to contract rhythmically when subjected to a
weak and continuous stimulus. He also calls attention to the rhythmic
contractions seen in the Protozoa, the snail’s heart, etc. Finally,
physiologists are much inclined to explain the rhythmic contraction of
the heart and other involuntary muscles, in part, at least, as due to a
property of the contractile tissue.
_Margin, Radial Ganglia, Nerve_--Experiments 18, 21-23, 30.--Complete
removal of the margin did not stop pulsation; but the removal of the
radial ganglia stopped it permanently. While this experiment seems to
have been tried only once, yet, taking into consideration the results of
other operations, it would seem that the principal centers of spontaneity
reside in these ganglia. (It should here be remembered that the
interradial ganglia were probably removed at the removing of the margin.)
Cutting the nerve in the eight adradii caused the _pedalia_ to bend
inwards at right angles to their normal position but did not in the least
affect the coördination of the sides. When, however, the sides were cut
in the eight adradii to the base of the stomach, coördination for the
main part ceased, and each side pulsated in its own rhythm.
I have said that the principal centers of spontaneity reside in the
radial ganglia. Upon further thought this hardly seems warranted. No
doubt, among the principal motor centers must be placed the ganglionic
masses of the clubs, and the radial ganglia, together with the homologous
interradial ganglia, represent centers of equal value. I speak of these
two sets of ganglia as homologous, since strictly speaking, they both
belong to the margin, and the clubs at whose bases they lie probably
represent modified tentacles. Conant’s experiments leave us in the
dark as to the function of these ganglia. Next in order, it would
seem, are the ganglion cells in the suspensoria, as is suggested by
the contractions of an isolated side with a portion of a suspensorium
attached. (See previous head.) While we have seen that the frenula and
the velarium can contract by themselves, yet, I find no evidence that
these can impart their contractions to any adjacent tissue.
Conant’s results on cutting the nerve eight times and then continuing the
cuts to the base of the stomach are quite the same as Romanes and Eimer
obtained upon Aurelia. Romanes, however, concludes that in his Sarsia,
Tiaropsis, etc., coördination was broken when only short incisions were
made in the margin. Charybdea appears, then, to agree with Aurelia rather
than with the Hydromedusæ. Yet, since Romanes at first obtained similar
results to those of Charybdea on Sarsia, but on further experimenting
concluded that coördination had really been destroyed at the first
cutting, we cannot speak with certainty that coördination had not been
destroyed in Charybdea before the cuts had been continued to the base of
the stomach. I say not with certainty, because the injury to the bell
being slight, coördination may have been maintained on the principle of
a simultaneously (simultaneous for the octants) alternate exhaustion and
recovery of the contractile tissue on the principle of Romanes’ theory.
_Stimulation._--Romanes found when he stimulated a deganglionated bell
of a Hydromedusa, that it responded by a single contraction, while that
of a Scyphomedusa responded with several quite rhythmic contractions.
Charybdea in this respect agrees with the Scyphomedusæ. Romanes’ results
were also verified on Aurelia. (Experiments 12c, 15, 50, 51.)
_Activity of Charybdea._--In speaking of the activity of Charybdea, I
cannot do better than refer the reader to the notes. (Experiment 41.)
Conant remarks in his dissertation what an active swimmer Charybdea is,
and this is further borne out by his later observations.
_Temperature._--Ice in the water seemed to have no effect, except when
held against an animal, when a slowing of pulsation followed in a few
instances. On some pulsating actively in the sun the temperature of the
water was found to be 92° F. (Experiments 33-35.)
Conant does not tell us how cold the water became when he placed ice in
it, but judging from his results, it seems that he might have obtained
a decided slowing of pulsation if the water in which the medusæ swam
had been permitted to approach anywhere near the freezing point, say
35-40° F. Romanes obtained decided slowing of pulsation, and even
complete inhibition, on a bell of Aurelia, as also a lengthening of the
latent period on some strips cut from a bell of Aurelia, by lowering
the temperature of the water. Replacing Aurelia in warmer water had
the effect of immediate recovery and increased rhythm. In Aurelia,
raising the temperature increased the rhythm but diminished it when the
temperature of the water became 70-80° F. After a slowing of pulsation
due to such a rise of temperature, it would not quicken again when the
animal was placed in water of its normal temperature. Romanes explains
this by supposing that the tissue of the medusa had been permanently
injured by the abnormally high temperature. It would be interesting to
observe how the tropical Aurelia behaved under such treatment, seeing
that Charybdea pulsated actively and without apparent injury in water at
92° F. _Limnocodium_, noted by Romanes, and probably a tropical species,
lived happily in water at 85° F. in the lily house of the Royal Botanical
Society. The temperature of the water could be raised to 100° F. before
it proved fatal to this medusa. Such facts point to a decided difference
in the constitution of the protoplasm of tropical and temperate medusæ.
Romanes’ Sarsia became frantic when placed in milk-warm water.
While writing the above, I was led to wonder whether the temperature
of the water may not have been the stimulating influence in those
experiments on light (previously noted) in which the medusæ continued to
swim actively in the sunlight.
_Food and Feeding._--See Experiment 36.
I again make note of a few observations made by myself on the Olindiad.
A crustacean became entangled in the tentacles of a medusa; apparently
this wished to retain it, for the proboscis reached in the direction
of the crustacean, which, however, got away. I then placed, by means
of a needle, another small crustacean against one of the tentacles.
This was seized but not retained, for the animal pulsated and it was
washed away by the water. Twice I saw a good-sized crustacean in the
proboscis. In one instance the velum appeared to hold the part of the
crustacean not yet in the proboscis. I noticed another with a crustacean
wholly in the proboscis, which was much lengthened out, the upper part
of the crustacean being in the stomach. The next morning the crustacean
was wholly in the stomach and the proboscis normal. At 5.30 P. M. the
crustacean was ejected, nothing but the shell and some rubbish remaining.
These medusæ seem to pay no attention to being touched by one of their
kind, except to give a pulsation or two.
The proboscis appears very “intelligent” in its actions.[c] First, some
of the tentacles can be seen to contract and to bend inwards, then the
side next the tentacles contracts and the proboscis is seen to reach in
that direction. I could not see, however, what the irritant was.
_Occurrence of Charybdea_--Experiments 37-40.--Dr. Conant’s remarks
(“Cubomedusæ”) on the occurrence of Charybdea at the surface of quite
shallow water and near the shore (which is quite at variance with former
observations, that the Cubomedusæ are essentially deep-sea forms) are
further borne out by his observations at Port Antonio. As already noted
in the Introduction, Charybdea was here found in abundance in quite
shallow water and near shore, but on the bottom instead of at the
surface as at Port Henderson. It is possible that the animals had been
active near the surface earlier in the morning and that some unknown
conditions determined their settling to the bottom earlier in the former
place than in the latter.
Conant’s conjecture, “whether these were their natural conditions,
or whether the two forms,” Charybdea and Tripedalia, “were driven by
some chance from the deep ocean into the harbor and there found their
surroundings secondarily congenial, so to speak,” seems to be borne out
in favor of the former supposition (for Charybdea at least),--that these
are their natural conditions and that Charybdea Xaymacana is essentially
a shore form.
AURELIA AND POLYCLONIA (CASSIOPŒA)
Experiments 42-53.
Many of the observations on these forms relate to the rate of pulsation.
In an Aurelia, following the removal of a lithocyst, there was a pause
followed by pulsations. In about two minutes rhythmic pulsations were
renewed. Four minutes after the operation there were nineteen pulsations
to the half minute, while twenty minutes after there were only nine,
and these in groups of six and three. The normal rate of pulsation was
twenty-five to the half minute.
Polyclonia behaved much in the same manner as Aurelia. Upon the removal
of lithocyst pulsations continued, but in groups with short pauses. The
normal rate of pulsation was twenty-seven to the half minute, while three
minutes after the operation it was seventeen, and eleven minutes after,
fifteen to the half minute. The tissue connected with a removed lithocyst
gave contractions. Placing a Polyclonia in fresh sea-water more than
doubled the rate of pulsation, which, however, soon fell to the normal
rate, and lower in one instance. In small individuals the rhythm is
decidedly more rapid than in those of larger size. The few observations
on this point would seem to show that it is in inverse proportion to the
squares of the diameters of the bells.
The removal of a single oral arm or of the whole eight, in Polyclonia,
had much the same effect as the removal of a lithocyst: there was a
decided slowing of the rate of pulsation, while the immediate effect of
cutting was an acceleration or a return to near the normal rate. About
a day later this same animal had quite regained its normal rate of
pulsation and continued to live over two weeks. A long latent period
followed the cutting of an arm, before the stimulation of cutting
manifested itself.
An Aurelia, with all its lithocysts removed, still gave spontaneous
and coördinated contractions after allowing time for recovery from the
operation. This was the result in one instance, while in several others
only a few contractions were observed. Removal of the sixteen marginal
bodies (lithocysts) in a Cassiopœa produced paralysis for a time but
recovery soon followed. A Polyclonia with its entire margin removed was
paralyzed but had so far recovered in a day as to be able, at intervals,
to give spontaneous pulsations.