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 (Cassiopoea)

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 Cassiopoea 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.

The removed margin of a Polyclonia pulsated vigorously. This margin was 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 Cassiopoea.

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 Cassiopoea 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 Cassiopoea 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.

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, Cassiopoea, 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 Cassiopoea, 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.