then split so as to make a ring within a ring but connected at one point
by a small bridge of tissue. The waves of contraction, which always
originated on the ring with the lithocysts, passed the bridge to the
inner ring quite as Romanes experienced. The outer ring was next split
so as to separate the exumbral portion from the subumbral, when it was
found that the contractions always originated from the latter. Seven
days after its removal, this same margin was still alive and pulsating
vigorously, and broken-off pieces of the subumbral portion were pulsating
by themselves. Fifteen of the ganglia were removed. It was then found
that while most of the pulsations originated at the remaining ganglion,
now and then contractions originated in other parts where no ganglion
remained. Two days later this margin was still alive with contractions
originating as often from other parts as from the ganglion. A similar
observation was made on a margin of Cassiopœa.
A Polyclonia with the eight lithocysts of one side removed, to compare
with a normal one, gave no evidence of affected coördination.
An oral lobe from an Aurelia could give contractions some minutes after
removal.
In another Aurelia a circular cut was made about the base of the oral
lobes through the epithelium of the subumbrella. The animal could pulsate
well enough but coördination seemed a little affected, while in another
one with a like cut but semicircular, no effect was noticed.
These results on the removal of the lithocysts (and margin in Polyclonia)
in Aurelia, Polyclonia and Cassiopœa agree quite with those on Charybdea
and, of course, also with Romanes’ and Eimer’s results as to paralysis
and recovery following the removal of the lithocysts, or margin, in
Aurelia, Cyanea, etc. I recall no similar observations, however, on
removing a single lithocyst, and the question of an explanation for
the slowing of the rhythm thus brought about arises. Romanes gives as
an explanation for the slowing of the rhythm (Aurelia, Cyanea, etc.)
following the temporary acceleration upon removing the manubrium or a
portion from the center of the bell, as due to a lack of an afferent
stimulating influence upon the ganglia from the excised tissue. May
a similar explanation not serve to explain the slowing following the
removal of a single lithocyst, above noted? The removed lithocyst could
no longer give its efferent stimulus to the remaining ganglia nor to the
tissue, so that the former would have a weaker stimulating influence,
in consequence of which the latter (the contractile tissue) would be
deprived of a part of the original stimulus of the remaining ganglia as
also of that of the removed ganglion. The whole would thus result in
giving to the contractile tissue a weaker stimulus, which, again, would
require longer and greater recovery on the part of the tissue in order
to be set off by the stimulus at hand. This explanation is given on the
basis of Romanes’ theory of rhythmic contraction previously explained.
Of course, it may be suggested that the musculature had lost tonus,
due to the lack of influence of the removed ganglion (lithocyst), in
consequence of which there was a lowering of irritability on the part
of the contractile tissue. This would require a greater summation of
stimulating influence (Ganglionic theory of contraction) on the part of
the remaining ganglia to set it off. Again, the loss of irritability
on the part of the contractile tissue may have been due to a lack of
nutritive influence from the removed ganglion.
Romanes’ explanation, that the slowing of the rhythm following the
removal of the manubrium and central parts of the bell in Aurelia and
Cyanea is due to a lack of an afferent stimulus on the ganglia from the
removed tissue, likewise explains the similar results obtained by Conant
by removing the oral arms from Polyclonia.
The fact that a margin of Cassiopœa and also of Polyclonia, connected
with but one ganglion, often originated contractions in other parts as
well as from the ganglion, seems to show that motor centers resided
in the margin outside of the ganglia. This would be somewhat at
variance with Romanes’ conclusion, that no such centers existed in the
Scyphomedusæ. Conant does not state whether the Polyclonia margin in
question was kept in fresh sea-water or whether the water was not changed
during the seven days. If the latter is the case, then some poisonous
compounds may have been formed that acted as a stimulus much as weakly
acidulated water served Romanes in producing rhythmic contractions in
deganglionated bells.
Again, while it is true that no ganglia are known to exist in the margins
of the Scyphomedusæ outside of the ganglia in the marginal bodies, yet,
ganglion cells and nerve fibers are found in the subumbral part of the
margin as well as in the rest of the umbrella. And as I know no reason
why scattered ganglion cells may not function as ganglia, it is possible
that the contractions in question were spontaneous.
Finally, is it possible that the remaining ganglion originated the
contractions in different parts of the margin, thus acting at a distance
from the points at which contractions originated? Romanes gives an
instance in which he believed to have evidence that this was the case.
Upon a final consideration I am inclined to this latter explanation.
SUMMARY.
Summing up for Charybdea, we have seen that it is very sensitive to
light, strong light as also darkness inhibiting pulsations, while
moderate light stimulates it to activity. Also, a sudden change from
weaker to stronger light, or _vice versa_, may inhibit or stimulate to
activity respectively. This behavior of Charybdea seems to be correlated
with its habit of life on the bottom. We have no reason to doubt but that
the eyes of the sensory clubs are the seat of light sensation.
The experiments on equilibration are negative, giving us no certain
light on the function of the concretions, though it appears that they
may serve, in part at least, for keeping the sensory clubs properly
suspended. Their function in giving the animal sensations of space
relations is not, however, excluded.
Excision of the sensory clubs demonstrates that they are the seat of
important ganglionic centers, the removal of which results in temporary
paralysis and weakness. That they also are the seat of organs (eyes,
network-cells, concretions) that are of importance in giving information
in the life of Charybdea, is evident from the reaching motion of the
proboscis after the removal of the sensory clubs. Other centers of
spontaneity in their order of importance probably are: the radial ganglia
(one experiment); the interradial ganglia (?); the suspensoria, as shown
by their supplying stimuli to isolated pieces of the sides connected with
them; the frenula and the velarium, the latter of which gave contractions
when removed with the frenula or in pieces only. No evidence is given
that the frenula or the velarium can impart their contractions to other
tissue, though this seems probable for the former. The proboscis can also
contract of itself.
Reflexes between the velarium, frenula, subumbrella, sensory clubs,
nerve, and any one pedalium, on the one hand, and the pedalia on the
other hand, are very common, and point to the pedalia with the tentacles
as organs of defense and offense. The pedalia serve also as rudders in
swimming.
Finally, as judged by the results in this paper, Charybdea seems to
occupy, physiologically, a position intermediate between the Hydromedusæ
and the Scyphomedusæ. In its great activity as a swimmer, in its response
to light, and in its reflexes it is Hydromedusan, while in the paralysis
and recovery following the removal of its marginal bodies, as also in its
response with several pulsations instead of one, when a deganglionated
bell is stimulated, it is Scyphomedusan.
The observations on the Discomedusæ, Aurelia, Polyclonia, Cassiopœa,
demonstrate the existence of motor nerve centers in the marginal bodies;
but that other centers are present is shown by the recovery of pulsation
following the removal of the marginal bodies or the margin. These results
are mainly confirmatory of those of Romanes and Eimer. They differ from
these in the fact that margins of Polyclonia and Cassiopœa, with only one
ganglion attached, originated contractions distant from the ganglion.
Removing of a single lithocyst resulted in a slowing of pulsation, as did
also the removal of the oral lobes, though the immediate effect in the
latter case was an acceleration. Isolated pieces of the subumbrella could
contract.
DR. CONANT’S NOTES.
Below follow Dr. Conant’s notes. They are printed about as Conant left
them. Their order of succession, however, has been changed to bring
similar experiments together, while useless and often repeated ones
have been omitted, and short elliptical sentences completed. Where the
present writer wished to add any explanation, the same has been placed in
brackets.
CHARYBDEA.
_Light and Darkness._--1. Eight medusæ, in a deep glass jar and covered
by a black coat, except one inch around the top, were placed in the
dark-room.
a. When light from a lamp was thrown on the surface (one inch) layer, the
animals were active near the surface; when the light was withdrawn, one
or two were on the bottom and not moving but were probably pulsating.
b. After four or five minutes in the dark, three or four besides a feeble
one are on the bottom. It took about two minutes to get them all to
swim [by the lamp]. Of the three on the bottom, one, at any rate, was
not pulsating. [Three other attempts like a and b were made, with very
similar results.]
2. Experiment No. 1 was repeated several weeks later. Four in a large
round glass dish were placed in the dark-room. A lamp being held to the
dish all but one were found to be on the bottom. That one quickly went to
the bottom, while two of those on the bottom quickly came to the top. In
two or three minutes the one that had gone to the bottom began to pulsate
and at about the same time the other one that had remained on the bottom
also began to pulsate, while the two that had gone to the top stayed
there swimming very actively. [Repeated with like results.]
3. Fresh ones did not show the reaction to light after darkness so
well as did those in the experiments previously recorded. They were
experimented with about nine A. M., while usually they were tried later
in the day. I had rather suspected from previous work that they would not
react so well when fresh.
4. a. In walking with the jar (1) of jelly-fish of experiment 1 from
the dark-room to the back porch of the laboratory (fifty steps), in the
bright sun and a cool breeze, all were found upon entering the laboratory
door to have settled to the bottom and most of them to have ceased active
swimming. In five minutes two or three were swimming somewhat, and in
five minutes more all but one or two (eight in all) were swimming.
Walking with the jar about the laboratory did not suffice to make any
change in their swimming, nor did blowing on the surface make any
appreciable change.
b. Upon taking the jar to the back porch and placing it on the stone or
cement flags, in the shade and a cool breeze, in four minutes time all
were on the bottom not even pulsating.
Upon replacing them on the laboratory table all began to swim about at
once. [Repeated.]
c. The jar (1) was placed on the back porch again; in fifteen seconds
three were on the bottom; in one-half minute all but one. In three or
four minutes all were on the bottom, but two were swimming lively and the
others pulsating. In another minute all were swimming.
d. The jar (1) was tried again, not resting it on the flags but holding
it by my hands on the sides. The effect was just as quick; they stopped
pulsating at once. By the time I had got back to my table in the
laboratory, one was at the surface and another arrived just as the jar
was set down.
[Several other experiments of an order similar to those just noted were
tried, with very similar results.]
5. Two buckets stood side by side in the laboratory. One bucket (1) had
more Charybdeas in it than the other bucket (2), and also had more since
brought in (about an hour). The water of one (1) was also more discolored
and with more organic matter (sea weed, etc.). In the laboratory the
animals were active on the surface of both buckets. Placed in the
sunlight on the porch, no breeze, the sun slanting so that one side of
the water in the buckets was bright while the other side was shaded, the
jelly-fish in (1) went mostly to the bottom, while those in (2) seemed
unaffected though some showed a tendency to go to the bottom after a
longer exposure. The experiment with (1) was repeated and it took some
five minutes for them all to go to the bottom. In a few minutes after
replacing them in the laboratory several were active again on the surface.
6. Jar (a) with five large ones stood on my table; they were quite
active. Placed in the sun (no breeze), on the porch, one or two sank
to the bottom at once and the others seemed to slow their activities
somewhat but not very markedly. In a few minutes all were swimming,
apparently more actively than before, in the bright sunlight.
[In other experiments Conant shows that it is not the stimulus of walking
that causes them to swim when carried into the room, for they would not
swim when he walked with them on the porch. Also, he shows how they may
change, some swimming, others not, when left for some time in any one
place.]
7. In a tumbler were two pulsating very vigorously. Placed in the bright
sunlight, very little breeze now and then, they showed no change whatever.
8. Some in a jar were covered with a black coat. The coat was taken off,
and almost immediately they stopped pulsating, or pulsated but feebly,
and sank to the bottom. The coat was put on again with one part near the
bottom of the jar exposed. Almost at once, the animals, which were quite
motionless, pulsating but little, resumed pulsation, which became more
and more vigorous, and quickly swam to the top again. It seems plainly
to be a reaction to light. [Such experiments as this were repeated at
different times with very like results.]
9. A bucket with several bobbing actively on the surface was set out in a
smart shower, and the animals continued bobbing on the surface as before.
I could not see that they made the slightest attempt to go below.
There can be no doubt but that there is an individual difference in
sensitiveness to the reaction of light after darkness. E. g., I just
removed the coat from a dish with four in it; one went to the bottom at
once, another presently, a third remained active at the surface, the
fourth when noticed was on the bottom.
There is also a difference in the length of time they stay on the bottom
as well as in the quickness in the response to light. Some recover very
quickly, should say in less than a minute, and at once become very
active. Some stay for a long time and only resume activity upon the coat
being placed over them. Perhaps this explains some of the observations in
Experiment 1.
_Sensory Clubs._--10. All four concretions were removed and the animal
stood the operation well. It swam more restlessly, however, than others
did in the same surroundings. It seemed at first to show a trace of loss
of sense-perception. It swam up, and down again, more changeable than
those intact, which stay rather more constantly either on the bottom
or at the surface. This may, however, have been due solely to the
restlessness of the animal after the operation. Later it swam actively
for by far the most part on the surface only, which points to the truth
of the preceding statement.
It showed no reaction to _light_. A coat placed over the jar was removed,
when it was found to be on the surface and it remained there. This was
twice repeated. I noticed specially that on pushing the bell above the
surface of the water it at once turned and went deeper as the normal
animal does. Finally, given another a trial with removing the coat from
the jar, it went to the bottom as the normal animal usually does. After
this, when next seen, it was keeping to the bottom. [This experiment was
repeated on another occasion with almost identical results, no loss of
sense-perception being noticeable.]
Sometimes it seemed as if access of _light_ at removing the coat acted
as a stimulus to one or more of those that were quiescent on the bottom.
This was noticed again on the following day.
11. Two more were operated upon. These did not stand the operation well
and stayed on the bottom, one swimming, while eight hours later one
was in better condition (pulsating) than two left in the same dish for
comparison.
12. a. Three clubs were cut off leaving only the stalks. A temporary
paralysis of the power to swim was the immediate effect. Later it
partially recovered this power. The proboscis, which was previously
quiet, now showed convulsive twitchings and movements. It continued for
some time to move to one side and then the other (after short pauses of
varied length) as if to grasp some object. The lips of the _proboscis_
were also moving and at times expanding. Often the movements were towards
the side on which the club was uninjured.
b. The fourth club was next removed. A temporary paralysis as before
resulted, followed by a quick recovery of pulsation; but the animal was
now much weakened. The movement of the proboscis continued--shortening,
lips expanding, moving to this side or that. The pulsations of the bell
were kept up even when too weak to swim.
c. The sensory niches of this same animal were treated with 2.5 per cent.
acetic acid by means of a pipette. The stalks of all four clubs showed
white. Pulsations ceased. The velarium showed feeble local contractions.
The movements of the proboscis and suspensoria drawing down the stomach
continued. Upon stirring the animal it gave rather feeble, somewhat
convulsive pulsations with local (fibrillar) contractions; the pulsations
in some cases were pretty well coördinated, but were more on the
twitching kind.
13. Three clubs were removed. The animal pulsated well, only a little
less strongly, perhaps. After a minute or two the fourth club was
removed. It pulsated almost immediately, perhaps thirty seconds after the
operation. It swam very well and pulsated feebly five hours after the
operation.
14. One from jar (a) (Experiment 6) was operated upon. When the first
club was cut off there was a paralysis of pulsation followed by a quick
recovery. Cutting off the second club seemed to stimulate pulsation,
the third to diminish it; after cutting off the fourth club it still
pulsated. When placed in a large jar it pulsated on the bottom, but not
strong enough to swim. The pulsations were fairly regular and sometimes
seemed to occur in groups of two, but these groups were not well marked.
15. Another one from jar (a) was taken. One club was cut out, upon
which there was a very temporary paralysis followed by good pulsations
afterwards. The _proboscis_, as in all cases noticed, gave active
movements to this side and that side. These movements of the proboscis
were often very quick and definitely directed as if a well defined
stimulus were given. After the operation one _pedalium_ contracted so as
to be at a right angle to the main axis of the bell; shortly a second
pedalium also contracted. Placed in a small round dish the animal swam
actively.
A second club was removed, and it swam as well as before. After fifteen
minutes it was not swimming but pulsating against the jar. Upon stirring
it a little it swam vigorously ten to fifteen strokes and then stopped.
It seemed weak and its movements appeared not so definite, though this
might be due to weakness.
A third club was removed. The only change seemed to be rather greater
weakness.
After about five minutes the fourth club was removed. Paralysis of
pulsation followed. It had the power to contract its _pedalia_ when these
were rather vigorously stimulated with a needle. It also gave one feeble
pulsation when so stimulated.
16. The sensory clubs were removed from another. After removal of
the third one it still pulsated actively, but stopped completely and
apparently for good after the removal of the fourth club. Another one
stopped pulsating apparently for good upon removing the third club.
17. All four sensory clubs were removed from one, cutting as high up as
possible so as to remove the endodermal tract of nerve fibers of the
peduncle. It pulsated afterwards apparently the same as if the stalks had
been left intact.
18. A small piece surrounding a sensory club and including the _margin_
can contract by itself. The piece observed pulsated with quick pulsations
and rhythmically but intermittently. After a fresh cutting away of such
a piece, the portion of the _velarium_ attached was seen to contract
rhythmically, while the rest of the _subumbrella_ was not so seen. The
part of the subumbrella above the radial ganglion that was cut off did
not contract by itself. The same portion of the velarium cut off did give
contractions.
19. A sensory club with the surrounding region cut out pulsated
rhythmically; when the club was cut from the end of its stalk pulsation
stopped. This observation was repeated on another, and contractions were
seen after the removal of the club. A piece of the _subumbrella_ wall
from the same animal gave contractions now and then even after an hour.
20. The normal position of a sensory club seems to be with the concretion
almost at the lowermost end; often with it certainly lowermost, but
probably oftener with the perpendicular passing through the center of the
attachment of the club to its peduncle and just by the inner edge of the
concretion. The eyes point inwards.
When the animal is on its side the concretions are always quite
lowermost. When the animal was inverted the tendency was for the
concretions to be lowermost. In this position the eyes may point in
several directions. In one instance those of one club pointed rather
outwards, while of two other clubs they pointed more in the plane of the
body wall. (See also Experiments 24, 29.)
_Nerve._--21. Cutting the nerve eight times, once on each side of each
sensory club, produced no loss of coördination in pulsating. The animal
was weakened, however, by the operation, which was made drastic to insure
cutting the nerve; but it was still able to swim. This experiment was
repeated four times.
22. That coördination was continued after the nerve was cut was
proved beyond doubt by cutting from the edge up (eight times) so as
to perfectly separate the sensory clubs and the pedalia. Pulsations
continued synchronously in all four sides--not the slightest evidence
that one side contracted out of time with the others.
23. The eight cuts were made as in the preceding experiment with no loss
of coördination noted. When the cuts were carried up to the base of the
stomach, however, coördination ceased. The four side pieces seemed to
contract each in its own time. Only two sides could be observed at one
time, and they at any rate did not contract synchronously. One side often
gave two contractions while the other side rested or gave one.
Yet, a little later, three of the sides at any rate showed a pretty
good coördination. The fourth was smaller and did not seem to get into
the game much--it went more on its own schedule. The four pieces were
then cut apart and placed together under a dissecting microscope. No
coördination at all could be made out. No evidence, therefore, of any
definite rate of pulsation inherent in the sensory clubs.
Cutting the nerve causes the _pedalia_ to forcibly contract inwards.
_Side, Subumbrella._--24. A whole side was cut out, the transverse
cut being above the sensory organ so as to take off [leave off] the
radial ganglion also. This pulsated, or rather contracted, nicely. The
upper end had been cut just through the _suspensorium_. It especially
gave twitchings like the twitchings of the stomach. The piece was then
halved transversely, when the upper part containing the portion of the
suspensorium twitched as before while the lower part was not seen to
contract again. This was repeated with the same result, except that a
portion of the lower part gave a slight contraction several times. The
part that contracted was at the upper end of the piece, _i. e._, nearest
the _suspensorium_. The contractions were also more longitudinal than
transverse, as the regular contractions would be.
The piece connected with the sensory clubs of course pulsated nicely.
Upon cutting off the sensory club from the stalk, pulsation ceased, but
twitching of the _velarium_ continued. This was repeated with the same
effect.