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

by E. W. Berger

Romanes’ explanation, that the slowing of the rhythm following the removal of the manubrium and central parts of the bell in Aurelia and Cyanea is due to a lack of an afferent stimulus on the ganglia from the removed tissue, likewise explains the similar results obtained by Conant by removing the oral arms from Polyclonia.

The fact that a margin of Cassiopœa and also of Polyclonia, connected with but one ganglion, often originated contractions in other parts as well as from the ganglion, seems to show that motor centers resided in the margin outside of the ganglia. This would be somewhat at variance with Romanes’ conclusion, that no such centers existed in the Scyphomedusæ. Conant does not state whether the Polyclonia margin in question was kept in fresh sea-water or whether the water was not changed during the seven days. If the latter is the case, then some poisonous compounds may have been formed that acted as a stimulus much as weakly acidulated water served Romanes in producing rhythmic contractions in deganglionated bells.

Again, while it is true that no ganglia are known to exist in the margins of the Scyphomedusæ outside of the ganglia in the marginal bodies, yet, ganglion cells and nerve fibers are found in the subumbral part of the margin as well as in the rest of the umbrella. And as I know no reason why scattered ganglion cells may not function as ganglia, it is possible that the contractions in question were spontaneous.

Finally, is it possible that the remaining ganglion originated the contractions in different parts of the margin, thus acting at a distance from the points at which contractions originated? Romanes gives an instance in which he believed to have evidence that this was the case. Upon a final consideration I am inclined to this latter explanation.

Summary.

Summing up for Charybdea, we have seen that it is very sensitive to light, strong light as also darkness inhibiting pulsations, while moderate light stimulates it to activity. Also, a sudden change from weaker to stronger light, or vice versa, may inhibit or stimulate to activity respectively. This behavior of Charybdea seems to be correlated with its habit of life on the bottom. We have no reason to doubt but that the eyes of the sensory clubs are the seat of light sensation.

The experiments on equilibration are negative, giving us no certain light on the function of the concretions, though it appears that they may serve, in part at least, for keeping the sensory clubs properly suspended. Their function in giving the animal sensations of space relations is not, however, excluded.

Excision of the sensory clubs demonstrates that they are the seat of important ganglionic centers, the removal of which results in temporary paralysis and weakness. That they also are the seat of organs (eyes, network-cells, concretions) that are of importance in giving information in the life of Charybdea, is evident from the reaching motion of the proboscis after the removal of the sensory clubs. Other centers of spontaneity in their order of importance probably are: the radial ganglia (one experiment); the interradial ganglia (?); the suspensoria, as shown by their supplying stimuli to isolated pieces of the sides connected with them; the frenula and the velarium, the latter of which gave contractions when removed with the frenula or in pieces only. No evidence is given that the frenula or the velarium can impart their contractions to other tissue, though this seems probable for the former. The proboscis can also contract of itself.

Reflexes between the velarium, frenula, subumbrella, sensory clubs, nerve, and any one pedalium, on the one hand, and the pedalia on the other hand, are very common, and point to the pedalia with the tentacles as organs of defense and offense. The pedalia serve also as rudders in swimming.

Finally, as judged by the results in this paper, Charybdea seems to occupy, physiologically, a position intermediate between the Hydromedusæ and the Scyphomedusæ. In its great activity as a swimmer, in its response to light, and in its reflexes it is Hydromedusan, while in the paralysis and recovery following the removal of its marginal bodies, as also in its response with several pulsations instead of one, when a deganglionated bell is stimulated, it is Scyphomedusan.