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.

In the same animal, in cutting off the sides, the stomach was left, the cut being through the gastric ostium. The floor of the stomach was now cut off by cutting out the four interradial points of attachment. The stomach and the proboscis gave vigorous contractions and tied themselves all up so that I could not cut off the proboscis.

The four pieces of the floor of the stomach left on the interradii gave contractions nicely. The phacelli continued their squirming movements.

25. Cutting off the whole aboral end of the animal excites to very rapid pulsations of the remaining part. The stream, as shown by particles in the water, is apparently stronger out the aboral end than past the velarium.

It seems that I get no good evidence that the subumbrella is able to contract of itself without connection with special nerve centers. In the one case noted (Experiment 31) I could not be sure but that the part that contracted was intimately associated with the suspensorium or frenulum.

26. A piece of the subumbrella cut off and having, so far as I could determine, no connection with ganglia, frenula, or suspensoria, gave contractions. Another piece was not seen to contract.

A small piece of the subumbrella connected with a club can contract. The proboscis can give contractions of itself when cut off with the base of the stomach. Even a cut-off lip can twitch by itself. A portion of the subumbrella by itself also showed twitchings. (See also Experiments 18, 19, 25, 26, 29, 47, 49.)

Pedalia, Velarium, Radial and Interradial Ganglia.—27. The pedalia with their tentacles were cut off at their bases to insure cutting out the interradial ganglia. The animal could pulsate well enough, but intermittently and without much progress (the velarium, of course, being injured). Cutting one pedalium caused the others to contract.

28. When the pedalia were cut off from one, the power of direct motion was entirely gone. It swam in circles, turned summersaults, changed its course continually, the oral end getting ahead of the aboral end, or trying to do so. The whole power of balancing was gone. It seemed excited by the operation and swam continually. [Repeated.]

29. The pedalia can be made to contract inwards by stroking their outer edge with a needle. This was noted last year and has been seen several times this year. Their inner edge is not so sensitive.

Touching a sensory club caused the pedalia to contract inwards in two cases.

The pedalia could be made to contract by giving the subumbrella a prick,—generally a rather severe one was necessary. The upper part of the subumbrella seems not so sensitive as the lower part and the proboscis, and the base of the stomach did not give any reflex at all (two specimens). One of the two could be made to give the reflex only with much difficulty. This was a very lively one. It would even stand severe pricks on the nerve, or even through the region of the sensory clubs, without contracting the pedalia or stopping pulsations.

Cutting the frenula seemed not to affect the ability to swim well. Cutting in this region brings about the reflex of the pedalia.

In the preceding fish the velarium was cut away wholly in some places, in other places it was left only as ragged strips. The pedalia became very strongly contracted and the tentacles were brought inside the bell. Pulsations that seemed strong produced much less progress than with the velarium intact. [Repeated.]

30. One with the whole margin cut off still gave pulsations. Upon the removal of the region of the radial ganglia, however, pulsations were seen no more.

The velarium in the above continued to give twitchings. The four pedalia were cut off with plenty of the tissue at their bases to insure the removal of interradial ganglia, and twitchings of the velarium with irregular contractions continued. No full contraction all around the velarium was noticed. When all the tissue was trimmed off as nearly as possible down to the velarium, the latter still gave twitchings and irregular contractions as before,—even more so as if excited by the operation. The power of originating contractions evidently resides in the velarium or in the ganglion cells of the frenula just as it does in the proboscis and the floor of the stomach.

Small pieces cut from between the pedalium corners and the frenula, so as to have tissue on them from neither, could contract by themselves. (See also for Pedalia, Experiments 15, 23, 41b; Velarium 18, 41c.)

Tentacles.—31. A cut-off tentacle can contract by itself, sometimes with squirming contractions. A prick at either end can produce a forcible contraction. A slight prick at the distal end may produce a local contraction. The proximal end is more sensitive, but this difference is not very marked. One with only the tentacles removed seemed to be a little less able to guide itself well.

Proboscis, Stomach, Phacelli.—32. The lips of the proboscis are highly contractile by themselves. The movement of the stomach and the phacelli goes on, after the lips are cut off, with increased vigor, due to the stimulus of shock. The vigor and frequency of their contractions, however, diminish quicker than that of the cut-off lips. (See for Proboscis, 12, 15, 18, 26, 29; Stomach, 18, 24, 29, 31; Phacelli, 18, 24, 31.)

Temperature.—33. Temperature does not seem to have much effect. Some placed in a tumbler half full of water, in the bright sunlight, swam vigorously over three-fourths of an hour. The water was quite warm to the hand.

34. The above experiment was repeated with the same results. A thermometer placed in the water with them showed 92° F.; hung in the sun near by, it showed 94° F.

Ice in the water did not stop their pulsating temporarily or permanently, except that it did for a short time after being held against one. Even then it took some time (fifteen to twenty pulsations) before it produced any effect.

35. Ice placed in the water again showed no marked effect. They swam as lively as ever. Some, after pulsating against the ice for a little while, seemed to be less vigorous, but quickly recovered in another part of the jar. Others did not seem to be the least bit affected by contact with the ice.

Food and Feeding.—36. I tried to feed one. A red and a white copepod were put into the subumbrella cavity. No attempt to eat it was observed in either case, though the copepods remained in the subumbrella cavity for some time.

Animals found in the stomach of Charybdea: small fish were most frequently seen; at another time a small stomatopod; again, a small polychæte; small shrimps; amphipod.

Those taken on August 16th (3 to 4 P. M.) seemed to have, for the most part, food in the stomach, and this more so than those taken in the morning.

Occurrence of Charybdea.—37. In the first tow on the bottom (with a net made of mosquito-netting and weighted with rocks in order to sink it) the haul was forty. I do not think that we could have been towing more than four or five minutes. The time was about seven A. M. A light breeze was blowing and there had been a heavy shower a half-hour previous.

38. The usual time of towing was about 6.30 to 7.30 A. M. The water was four to five feet (1.2 to 1.5 m.) nearest shore but deeper farther out. At this time of day one could count on getting plenty of the larger sized (15 to 20 mm.), many small ones, but very few of the smallest. This was the experience of several mornings.

On August 12th I towed about nine A. M., and got but few of the larger sized, many small ones, and very many of the smallest.

The next day (7.00 to 7.45 A. M.) those obtained were mostly of the larger size. On the same day (3 P. M.) others of the party towed at the same place and obtained but few.

On another day I towed in the afternoon (3 to 4 P. M.) and obtained great numbers as I usually did in the morning.

39. We towed about 7.30 to 8.30 at night. Very few Charybdeæ were taken. On this evening we towed five times in the same locality, and obtained but seven or eight specimens. Towing with the same net on our way home, it was filled with Aureliæ and five or six Charybdeæ. It seems as if Charybdea came to the surface at night. Those towed in the evening were dead the next morning.

The next morning Richard, our colored attendant, towed from 5.30 to 6.30. There were heavy showers. The usual find of large and medium ones was obtained. There were only two with planulae.

40. The material of September 2nd was obtained about six A. M. They were mostly of large size. In all only fifteen or twenty were taken. Richard explained the small number by saying that the bottom had changed in the locality where we usually towed and that he got no weeds in his net, but mud.

The next day more were brought in by Richard (6.30 A. M.) There were rather more than yesterday but the quality was the same. There were three with planulae.

On another morning Richard brought in a great many, about a hundred. Among these there were three with planulae (light-colored and budding); on a previous day there was one with the reddish-brown kind and with a mouth.

Activity of Charybdea.—41. a. About five o’clock in the morning a Charybdea was taken in the tow. It was in good condition swimming incessantly round and round without change of direction, in a jar of about twenty centimeters in diameter. It came to the surface every now and then, after eight to fifteen pulsations. The tentacles and the phacelli were of a lilac shade. If a pencil was placed in its way it would pulsate against it repeatedly without any effort to dodge around it.

At 10.15 it went around the dish in eight seconds, taking eighteen or nineteen pulsations. If a bright platinum spatula or a black pencil was placed in its circuit it would repeatedly butt against it each time it came around. After the second or third pulsation against it, however, it seemed to have some sense to change its direction.

b. The pedalia have no perceptible action of their own. They move inwards slightly toward the axis at each pulsation, but scarcely as much as one would suppose from their attachment to the pulsating margin. It seems as if they were for “winging” the moving animal more than for anything else.

c. The velarium is loose and it flaps. It seems to take part in swimming something more than the passive diaphragm function,—i. e., it straightens out during the recovery after each contraction of the bell.

Aurelia and Polyclonia.

[The following experiments were performed at Port Henderson, Jamaica, in 1896.]

42. May 12th. An Aurelia was pulsating normally at the rate of twenty-five or twenty-six pulsations to the half-minute. One lithocyst was cut out, when a few contractions, evidently caused by the stimulus of cutting, followed; then, rest. In the first minute there were only about five pulsations. In two or three minutes rhythmic pulsations were resumed. Four minutes after the cutting there were nineteen pulsations to the half-minute. About twenty minutes after there were nine to the half-minute, in groups of six and three.

A Polyclonia, about four and one-half inches (115 mm.) in diameter, gave twenty-six or twenty-seven regular pulsations to the half-minute. After one otocyst was removed, pulsations continued, but in groups with intervals of pause: e. g., thirteen, pause; ten, pause; six. Three minutes after the removal of the lithocyst there were 5, 3, 1, 3, 5, or seventeen pulsations to the half-minute. Eleven minutes after the operation there were fifteen to the half-minute. The removed lithocyst and surrounding tissue gave contractions.

43. May 13th. The Aurelia was in rather poor condition but would pulsate upon being stirred. The other seven lithocysts were removed when only a few contractions originated thereafter.

The Polyclonia was in good condition, but was pulsating only intermittently when first seen in the morning. When the remaining seven lithocysts were cut out and no more pulsations were observed, the oral arms could still move.

May 14th. Both were found dead upon returning in the evening.

44. May 15th. An Aurelia and a Polyclonia were taken in the morning. The Aurelia was two and one-half to three inches (62.5-75 mm.) in diameter, with three tufts of phacelli, three oral arms and seven lithocysts. The Polyclonia was normal and seven or eight inches (175-200 mm.) in diameter.

In the Aurelia all the lithocysts were removed. Spontaneous and coördinated contractions could still occur after time had been allowed for the shock from the operation to pass away. The next day the animal was still alive and pulsating, but ragged, and the next day following was quite dead.

In the Polyclonia the normal rhythm was fourteen pulsations to the minute. Some pulsations were apparently quicker than others and the intervals were not the same. Thirteen, ten, and twelve pulsations were also counted. After putting the animal into fresh sea-water, it pulsated thirty-three to the minute. Six minutes later it was still pulsating at the same rate, while in four minutes more eleven pulsations, many of which were in groups of two, were noted. In five minutes more it pulsated eleven times to the minute with only one double pulsation. One oral arm was then cut off and the rhythm counted about one minute afterward—fourteen pulsations, then a pause of fifteen seconds, then two pulsations, in all sixteen to the minute were counted. About ten minutes later there were eight pulsations, two or three minutes later only three, while in two or three minutes more only three. There was a long latent period—two or three seconds—before the stimulation of cutting off the arm made itself evident in the rhythm.

A second oral lobe was removed. Then there followed twenty-four pulsations, a pause of two seconds, and two pulsations, in all twenty-six pulsations to a minute. The rate of pulsation soon fell to the previously abnormal low rate.

Third lobe removed: 21 pulsations in first half minute and then 16, or 37 per minute.

Fourth lobe removed: 17 pulsations in first half-minute plus 13 gives 30 for the minute.

No difference in the coördination of the animal was shown as a result of the removal of one-half the number of oral arms.

Fifth lobe removed: 17 pulsations plus 15 equals 32 to the minute.

Sixth lobe removed: 17 in first half-minute plus 4 in the second half-minute gives 21 pulsations for the minute.

Seventh lobe removed: 17 plus 9, or 26 per minute.

In all these instances the rhythm in the second half of the first minute was irregular and intermittent.

Seventeen and then seven pulsations were provoked after the animal had become quiescent, or nearly so, by merely handling it.

45. Eighth oral lobe was removed and pulsations stopped. The next day the animal was in good condition. The pulsations counted in the evening were 12, 14, 14, 11, per minute. The rhythm was not regular; there was a tendency to groups of twos, threes, or more, but no prolonged intervals of rest were observed. When placed into fresh sea-water, the pulsations were fourteen to the half-minute or twenty-six to the minute; seventeen to the half-minute, and thirty-three to the minute were also counted. This specimen gave spontaneous contractions during two weeks, after which it was thrown out, the aboral end being eaten through and little or no regeneration having taken place.

46. Two more were operated upon: A. Its rhythm was 18, 14, 17. Its entire margin was cut off. The separate pieces of the margin pulsated, 6, 7, 4, 6, 7, 9. The animal seemed paralyzed by the operation; it responded by a contraction now and then to stimulation but gave no spontaneous pulsations. B. Its rhythm was 17, 15, 12, 12. All its oral arms were removed. Its rhythm was only raised to seventeen and not perfect. In twenty-five minutes it had fallen to eleven, in four hours to ten pulsations [per minute].

May 22nd. A and B are living as also the pieces of the margin of A; all are giving spontaneous pulsations now and then at comparatively long intervals—even A, with its margin removed.

May 26th. Everything is still living. The one with the margin cut (A) counted sixteen and nineteen pulsations per minute, though this was not kept up all the time.

June 2nd. A and B and pieces are still living and contracting spontaneously. It is now two weeks, and they were thrown out eaten through at the aboral end with little or no regeneration.

47. The margin was cut off another one (C) and it was then paralyzed. The margin contracted vigorously by itself. The margin was next split, but a connection of about one-half an inch wide was left between the two rings. Over this bridge the contractions passed from the outer and inner ring. The inner ring did not originate any contractions. Both rings were then cut near their connecting bridge of tissue and the larger ring with the marginal bodies was split longitudinally so as to separate the exumbral from the subumbral portion. It was found that the contractions started only from the subumbral portion while the exumbral portion did not contract at all.

June 5th. Five of the eight small pieces of C were not seen to contract either to-day or yesterday. A slow rotary motion was observed in some of the pieces suggesting ciliation, but no cilia or currents pointing to ciliation were seen with a low power. C was seen to pulsate spontaneously. Possibly it did yesterday but it was not watched closely. A piece of the subumbral surface of C broken off (not from the margin) was found to contract spontaneously.

48. June 6th. In a fresh one (D) from Port Royal, the eight lithocysts of one side were removed in order to compare its movements with an intact one. Coördination was apparently unaffected.

June 9th. The margin of C is still pulsating vigorously. Parts of the subumbrella broken loose from the strip pulsated by themselves now and then. Fifteen lithocysts were removed, leaving only one at the end of the strip. It was found that with this single ganglion (lithocyst) left, and originating most of the contractions, now and then a contraction would originate at another part of the strip where there was no ganglion. Three days later contractions originated as often from other parts as from the ganglion.

Cassiopœa.

[The remaining experiments were all performed in 1897, at Port Antonio.]

49. Removal of the sixteen marginal bodies caused paralysis for a time; then recovery followed.

Contraction was limited to the subumbrella.

A portion of the subumbrella not from the margin can contract by itself as well as a portion of the margin with the marginal bodies (lithocysts).

In the margin cut off as a strip with only one marginal body attached at one end, contractions sometimes started from the opposite end.

Aurelia.

50. Size, seventeen or eighteen millimeters. Pulsations, thirty-two. Lithocysts, nine. The operation consisted in the removal of the concretions with as little injury to the pigmented parts of the marginal bodies as possible. One whole marginal body, however, was removed in the operation. Soon after the operation the pulsations were 28, 26, 20, 20, per minute.

Another one; size fifteen millimeters. Pulsations were forty per minute. The operation consisted in the removal of the concretions and pigmented parts of the marginal bodies with as little injury to the adjoining parts as possible. After the operation it seemed as if the intervals between the pulsations were irregular,—not a series at regular intervals. An hour or so after the operation the pulsations were very intermittent. During the afternoon it was not seen to pulsate except when it was stirred up, when six or seven vigorous pulsations followed. These, however, were rather aimless.

51. One sensory club (marginal body) was cut out, including its basal part also. In one or two other cases more or less injury was done to adjoining parts also. Pulsations ceased upon the removal of the last club, but upon placing it in an aquarium and allowing it to come to rest for two or three minutes, pulsations were now and then seen. In the evening, this one and another did not pulsate except when stirred, when they pulsated with good progress.

52. A circular cut, about two inches in diameter, was made through the epithelium of the subumbrella around the base of the oral lobes. The animal pulsated well enough, but the contractions seemed not so simultaneous in all parts of the margin as normally. After a few days it had partly regenerated but died. One of the oral lobes cut off had some power of contraction, and this some time after the operation. A similar cut, but semicircular, made no difference between the contractions of the two halves.

53. The whole region of the sensory clubs was cut out when the animal was not seen to pulsate again, except in the evening, when pulsations were observed. The oral lobes also moved.

HISTOLOGICAL.

Method.—The following results on the histology of the sensory clubs, their eyes, and the tentacles, as already noted, were obtained from some of Dr. Conant’s preserved material. These results relate almost wholly to Charybdea, with only a few references to Tripedalia, noted in their proper place.

A portion of this material was killed after keeping the animals in the dark for some time, for the purpose of discovering any changes in the pigment of the eyes. I believe that a retraction of the pigment of the long pigment cells that project between the prisms and pyramids of the vitreous body in the retina of the distal complex eye is very evident in eyes killed in the dark. (But more on this below.)

I obtained my best results from the material preserved in saturated corrosive sublimate, to which had been added (5 to 10 per cent.) acetic acid. This also was Conant’s experience in his previous work on Charybdea and Tripedalia.

My best sections were obtained by embedding the sensory clubs in celoidin, passing the little blocks of celoidin with the sensory clubs into chloroform until perfectly transparent, and then into paraffine. I then cut sections as we ordinarily cut paraffine sections, mounted and stained them on the slide. My purpose in using this method was to avoid the displacement of the vitreous bodies of the eyes during embedding and cutting. This object was fully realized and more besides. Since the sections cut by the celoidin-paraffine method gave me so decidedly the best differentiation of the axial fibers of the retinal cells, as also of the cilia, basal bodies, etc., I am inclined to believe that the celoidin was in part responsible for this differentiation.

Most of my series were cut 4 µ in thickness. All in all I cut sixty-five clubs besides making some maceration preparations from material preserved for that purpose. These sixty-five series represent material from fourteen bottles. As a whole, my material was good, but the material from one bottle was decidedly superior for showing the axial fibers of the prisms and pyramids of the retinal cells. This shows the advantage of plenty of material. It will be evident that I had plenty of material.

I found iron-hæmatoxylin the most satisfactory stain. I stained for a shorter or a longer time—one-half to several hours and longer—and then washed out the sections until under a low power of magnification they appeared quite unstained, the nuclei and a few other parts only appearing darkly stained.

Depigmentation I practiced but little. I obtained many of my series almost wholly unpigmented, especially those I cut last. Others, of course, were very heavily pigmented. I am not certain but that alcohol slowly dissolves out the pigment after a long period of preservation. Slight variations in the technique of killing and preserving may also, perhaps, determine the stability or solubility of the pigment, as, of course, also the condition of the pigment at the time of killing.

Anatomy.—For a short epitome of the anatomy of a Cubomedusa and of a Cubomedusan sensory club see p. 2 of the Introduction.

The Distal Complex Eye—General.—The distal (larger) complex eye (Fig. 7) and the proximal (smaller) complex eye (Fig. 13) are so named to distinguish them from the lateral simple eyes of the clubs. The distal complex eye consists of the following parts: a cellular cornea, continuous with the epithelium of the sensory club; a cellular lens (externally cellular and internally often quite homogeneous) immediately beneath the cornea; a homogeneous capsule just internal from the lens, and evidently a secretion from the lens cells; a vitreous body composed primarily of prisms and pyramids just beneath the capsule; and a retina of pigmented cells, with subretinal nerve tissue, ganglion cells and fibers. To my knowledge all observers (except Carrière, who missed the capsule) are quite agreed on the anatomical structure of the distal complex eye as also on the proximal complex eye and the lateral simple eyes.[d] It is on the histological structure of some of the various parts that differences exist.

Cornea.—Little need be said on the cornea except that it consists of flattened cells applied to the outer surface of the lens. It is continuous with the epithelium of the club and evidently a modified portion of this epithelium (Fig. 7). All observers conform to this statement.

The Lens.—The lens is of cellular origin, but in its interior the cells are often so changed—absence of nuclei, cell walls, and protoplasmic structure—as to make a mass quite homogeneous and structureless. While this internal mass sometimes shows practically no structure, yet at other times it is found broken up into masses much the size and shape of cells but without nuclei, while again, cells with nuclei may be quite evident. This occasional breaking up of this mass is evidently predetermined by its original cell structure. Iron-hæmatoxylin stains this inner mass very dark and it is difficult to wash out the stain. Borax carmine and Lyons blue give the best results on the lenses. In figure 7 the lens of the distal complex eye is shown as quite homogeneous internally, while in figure 13 (proximal complex eye) it is drawn cellular. In this latter lens the inner cells are quite round and nucleated as they may also appear in the distal eye. What I have said applies equally to the lenses of both complex eyes, though the cellular nature of the inside of the lens is more readily demonstrated in the proximal eye.

It appears that it is in younger specimens that the central mass of the lens shows the cellular structure best, and that as the animal grows older this structure is more and more lost until no trace of it remains. As concerns most of my series I could not well determine which were from younger and which from older individuals, yet, several series of quite small (5 mm.) and therefore young animals, in which the eyes were so small that the lenses were compassed into less than half a dozen sections, the cellular structure of the lens was very evident.

The external cells of the lens form a spherical shell (both complex eyes) which, in section, shows as a hollow ring (Figs. 7, 13). The thicker ends of these cells lie at the inner (toward the capsule) half of the sphere and the cells taper toward the corneal surface, dovetailing laterally with their immediate neighbors as also distally with those from the opposite side of the sphere. The thicker inner ends of the cells contain the large nuclei with nucleoli. At a point (* Figs. 7 and 13) on the inner (next the capsule) surface of the lens the cells only approximate each other and thus leave a place which is easily broken through, as is shown by portions (drops, probably representing cells or portions of cells) of the mass within the lens becoming squeezed out into the substance of the capsule and the vitreous body, and found occasionally also among the cells of the retina. A considerable portion of the inside of the lens may be found thus squeezed out, and its path can often be traced. This phenomenon is evidently brought about by a contraction of the shell of the lens during fixation and before the inside of the lens has become hardened.

In origin the lens is evidently ectodermal, originating from an ectodermal invagination which becomes pinched off as a hollow sphere, the outer (i. e. next the cornea) half of which becomes the lens, the inner half the retina (i. e. vitreous body plus the so called retina). (See Retina.) The transition from retinal to lens cells is quite readily made out at the lower side of Fig. 7, but the corresponding structure on the upper left side is not so manifest. It is further evident that the lens is again an invagination into this sphere, and the point at which the lens cells approximate (where the central mass of the lens may be squeezed out as above described) represents the place of pinching off of the original lens-retina sphere. It appears, then, that the lens is formed in the lens-retina sphere in the following manner: The cells of the secondary invagination going to form the lens begin to lengthen distally (i. e. toward the cornea) during their invagination to form a hollow sphere, at the same time dovetailing with each other and budding off cells to form the inside of the lens (Figs. 7, 13).

At the lower side of the lens, near the margin of the retina, the cells of the lens are slightly indented or pushed inwards (Fig. 7, ind.). I believe this to be due to the weight of the lens in the normal position of the club, when the lens rests against the margin of the retina and the capsule and adjacent tissue.

Anticipating the description of the retina, it may here be added, that the retina is formed from the inner half of the lens-retina sphere. The cells of this portion of the sphere become differentiated into prism cells, pyramid cells, and long pigment cells, while laterally, beyond the margin of the vitreous body, they are differentiated into pigmented iris cells (Figs. 7, 6a).

Above are my results on the lens. Haake[2] speaks of the lens as consisting of a cellular “Kern” with a covering of lamellated cells. Carrière describes it as cellular and filled internally with a “Gerinsel,” or coagulation. Carrière and Haake are each in part right. Claus describes it as wholly cellular. Schewiakoff regards the lens as wholly cellular, and like Claus has not noted that internally this cell structure may be quite obliterated. Schewiakoff regards the lens and retina as formed from an invaginated sphere, and shows the transition from the lens cells into retinal cells as I have figured. Conant also gives the structure of the lens for the complex eyes as cellular but missed the change of structure that the interior of the lens may undergo.

The Capsule.—The capsule of the lens (Figs. 4, 7) lies immediately below (inward from) the lens. In structure it is homogeneous, except for certain fibers from the long pigment cells of the retina that traverse it, while sometimes also other fibers can be seen which, possibly, are branches from the fibers just mentioned or continuations from the fine fibers of the prism cells of the retina soon to be described. I have, however, no evidence that the fibers from the prism cells extend beyond the prisms in whose axis they lie. The capsule lies very closely applied to the lens, never becoming separated from it in sections, and is, hence, regarded as a secretion from the lens cells. Just what its function may be is difficult to surmise. The proximal complex eye possesses no capsule. I have thought, however, that if the lens should be adjustable, the capsule might serve as a protection to the prisms of the vitreous portion of the retina during the adjusting movements of the lens. (But more on this below.) To my knowledge all previous observers are quite agreed on the structure of the capsule. Carrière and Haake, however, missed it altogether.

Retina.—While I have enumerated (following previous observers) the vitreous body and the so-called retina as distinct parts, yet, as the sequel will show, they are, histologically, different parts of the same thing—namely the sensorium proper of the eye—and I propose to use the term retina for both taken together, while I retain the expression vitreous body (as hitherto used) for the vitreous portion of the retina. This simplifies matters; and using a word that is already used for analogous structures of other eyes (vertebrates, anthropods, molluscs) is conducive to clearness. I have been tempted, furthermore, to use the words rods and cones for the prisms and pyramids that I find in the vitreous bodies of the retinas of the complex eyes. But since the prisms in reality approximate prisms and the pyramids pyramids, in their shape, I have decided to retain the words prism and pyramid for these structures. The former of these terms (prism) was first used by Conant in his description of the complex eyes.

What I shall call the retina, then, in the distal and proximal complex eyes of Charybdea, consists of three kinds of elements: the prism cells, the pyramid cells, and the long pigment cells. (Figs. 4, 7, 22, prc, pyrc, lp.) We may also describe the retina as composed of three zones: the vitreous zone (vitreous body of authors), the pigmented zone, and the nuclear zone. (Figs. 4, 7, 22, vb, pz, nz.)

The cells composing the retina form a single layer in the shape of a hollow cup, into which cup the lens with its capsule fits. (Fig. 7.) This single layer of cells takes in the thickness of the vitreous zone, the pigmented zone, and the nuclear zone. Indeed, the distinctions vitreous zone (vitreous body), pigmented zone, and nuclear zone characterize three topographical regions of the retinal cells.

That the retina is made up of three kinds of cells is most readily demonstrated in transverse sections through the vitreous body. Fig. 1 is such a section, taken quite near the pigmented zone (at about the level x, Fig. 4). Three different kinds of areas are readily made out in such a section. The more numerous areas (pr) are transverse sections of the distal prisms of the prism cells, the less numerous and lighter areas (pyr) are transverse sections of the pyramids of the pyramid cells, and the large oval heavily pigmented areas (lp) are the transverse sections of the long pigment cells. The dots within the two first named areas represent fine fibers in the axes of the prism and pyramid cells, to be described below. The presence of three kinds of cells can again be readily seen in such Figs. as 4 and 7, in which the elements of the retina are cut parallel to their long axis. (Fig. 22.) Again, a transverse section through the most distal part of the pigmented zone of a slightly pigmented retina (Fig. 2) also shows us the presence of three kinds of elements. The larger and more heavily pigmented areas (lp) are the long pigment cells; the smaller, lighter areas (pyrc) with a central dot are the pyramid cells, and the more numerous dots, with no definite polygonal areas outlined about them (prc), belong to the prism cells. Thus, I believe, we have conclusive evidence of the existence of three kinds of cells in the retina of the distal complex eye.

(a) The prism cells are the more numerous, and, as the name implies, end distally in a vitreous polygonal prism (Figs. 4, 7, 22, pr). The prismatic structure of the vitreous body is also shown in Figs. 10 and 11, which are drawn from a macerated preparation of Conant’s. (See the descriptions of these figures.)

In Figs. 4 and 7 the prism cells correspond to the cells with the darker nuclei (npr); in Fig. 2 they are represented by the dots without defined polygonal areas about them (prc), and in Fig. 1 by the most numerous areas (pr). These cells, then, consist of a centrad portion with nucleus, a pigmented portion with granules of a dark-brown pigment, distal from the nucleus, and a distal vitreous prism which extends to the capsule of the lens.

In the axis of each prism is a fine darkly-staining fibril extending the entire length of the prism. I found no good evidence that this fiber extends into the capsule. Centrad this fiber is continued through the pigmented part of its cell and approaches to or near the nucleus (Fig. 2, dots without defined polygonal areas; Fig. 7, part of retina left unpigmented). In some instances I could trace this fiber quite to the nucleus, while in others it ended before reaching the nucleus or a little to one side of it. I am inclined to believe, however, that it extends past the nucleus and is continued as a nerve fiber. I believe this to be so because the fiber is evidently sensory, and a priori we should expect it to be so continued. Further, I find decided evidence in sections of the simple eyes to show that the fibers there extend past the nucleus into the subretinal tissue where I could not trace them farther. (Fig. 16.) Again, that the flagella of the epithelial cells of the club are also continued into the cells, in some instances could be traced past the nuclei (Figs. 12 and 26), and the fact, too, that the retinal cups of the eyes represent invaginated epithelium (the axial fibers of the prisms are hence cilia?)—all this leads me to believe that the axial fibers of the prism-cells extend centrad past the nuclei through their cells and are continued as nerve-fibers. (See below under pyramid-cells and under epithelium). Immediately upon entering the pigmented part of its cell the axial fiber of a prism-cell has a dumbbell-shaped enlargement which lies quite at the distal edge of the pigmented part of the cell (Fig. 7, unpigmented part of figure). This, of course, can be seen only in unpigmented retinas. This dumbbell-shaped body, (Basalkörperchen of Apathy), which name I give it, since it evidently is homologous to the basal bodies described by others for the cilia of epithelia, can be most beautifully seen as two minute spheres lying close together and in line with the nucleus. These two little spheres of the basal bodies put to the test the highest powers of the microscope; but, when, after a prolonged and careful study, one satisfies himself of their existence and exact shape, the very difficulty with which they are resolved adds a zest to be appreciated. The length of a basal body is about one-fifth to one-fourth that of the nuclei of the prism-cells.

The structure of the nuclei of the prism-cells is that of a dense network (Figs. 4, 7, npr) which stains dark with hæmatoxylin. A nucleolus can often be seen in these nuclei. In some few series, again, these nuclei did not show a network-like structure, but the chromatin was arranged in masses (Fig. 5, npr). These nuclei can usually be distinguished from those of the other cells of the retina by their denser, darker-staining network (Figs. 4, 7, npr), or as shown in Fig. 5 (npr). Their denser structure and staining capacity are a distinguishing characteristic of the nuclei of the prism-cells. I must add, however, that not in every series is this apparent.

That portion of a prism-cell that contains the nucleus rarely contains any pigment; and when pigment is present, I believe that it has been dissolved in from the pigmented zone. The nucleus, again, lies a little centrad from the pigmented part of its cell, so that an unpigmented zone is seen in the retina between the pigmented zone and the row of nuclei (Figs. 4, 7, 22).