Physiology and histology of the Cubomedusæ / including Dr. F.S. Conant's notes on the physiology

by E. W. Berger

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.