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.