OBSERVATIONS AND EXPERIMENTS ON THE PHYSIOLOGY OF MEDUSAE

Abstract

1. Studies were made in Puget Sound on several medusae belonging to the groups Anthomedusae (Stomotoca, Sarsia), Leptomedusae (Aequorea, Halistaura, Phialidium), and Stauromedusae (Haliclystus).2. The water content was determined for four species (Aequorea, Halistaura, Phialidium, Sarsia) and found to range from 96.5 to 97 per cent (salinity of the sea water 3.09 per cent). Evidence was obtained that the water content declines slightly with increasing size.3. Activities are limited and responses cannot be elicited with dependable regularity.4. All species observed have alternate periods of pulsation and floating; in general these periods bear no absolute or relative time duration to each other.5. Behavior is correlated with morphology and hence shows characteristic differences between the different groups.6. Mechanical or chemical stimulation, when effective, elicits either an escape reaction or the feeding reaction.7. The escape reaction may consist of bell pulsations but to stronger stimuli a general contraction, termed crumpling, accompanied by cessation of swimming, is given. Aequorea is anatomically incapable of this escape reaction because of its thick stiff bell.8. The feeding reaction consists in the Leptomedusae and Haliclystus of bending the stimulated region of the margin to the manubrium which also moves to meet the inbent margin. In the Anthomedusae it consists of turning the long manubrium in the direction of stimulation.9. Food was traced through the gastrovascular system by feeding bits of animal flesh coated with carmine. Within half an hour after feeding, food begins to spread along the radial canals and in two or three hours occupies the entire gastrovascular system.10. The principal sites of intracellular digestion are the lining epithelium of the manubrium, stomach, and tentacular bulbs. Radial, circular, and tentacular canals play a minor rôle. Those portions of the radial canals adjacent to gonads (Leptomedusae) are much more active in intracellular digestion than radial canals elsewhere.11. No definitely directed flagellar currents could be observed in the gastrovascular system.12. Strands of carmine-containing mucus were seen to be extruded from the so-called excretory pores of the radial canals (Aequorea).13. The fluid from the stomach of Aequorea is usually considerably more acid than sea water (to pH 7.2, mostly 7.4-7.6). It contains a proteolytic and a lipolytic enzyme but appeared to be devoid of diastases.14. Feeding and escape reactions of Haliclystus (a sessile stauromedusan) are similar to those of Leptomedusae. No function could be found for the anchors; the animal gave no response to chemical or mechanical stimulation of the anchors nor were they used for adhesion.15. The tentacular bulbs of hydromedusae function as depots for the manufacture and storage of nematocysts, as organs of general sensory perception, and as important sites of intracellular digestion. They are not photoreceptors although in Anthomedusae they bear the ocelli when these are present. The tentacular bulbs of Gonionemus are devoid of differentiated photoreceptors.