OBSERVATIONS AND EXPERIMENTS ON THE PHYSIOLOGY OF MEDUSAE

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Abstract
The water content of 4 spp. of hydromedusae was 96.5-97% (salinity of sea 3.09%); it decreases slightly with increasing size. All spp. have alternate periods of pulsation and floating. Mechanical or chemical stimulation, if effective, evokes either an escape or a feeding reaction. The escape reaction may consist of bell pulsations but usually comprises a contraction into the smallest compass, cessation of pulsation, and sinking. In the Anthomedusae the feeding reaction consists in bending the long manubrium towards the stimulated area; in the Leptomedusae, the stimulated region of the margin bends inward to touch the manubrium. Food was traced through the gastrovascular system by feeding bits of animal flesh coated with carmine; in 1/2 hr. it spreads along the radial canals and in 2-3 hrs. occupies the entire system. Flagella are active in the canals but no definitely directed currents were seen. The chief sites of intracellular digestion are the manubrium, stomach, and tentacular bulbs; radial and circular canals play a minor role except regions of the radial canals adjacent to gonads. Strands of carmine-containing mucus were ejected from the so-called excretory pores of Aequorea. Stomach fluid of Aequorea was acid (mostly pH 7.4-7.6) and contained protease and lipase but no amylase. The sessile seyphozoan Haliclystus reacts like Leptomedusae; no function could be found for the supposedly adhesive anchors. The tentacular bulbs of hydromedusae are important as centers of nematocyst manufacture and regions of intracellular digestion; they boar no photoreceptors in Gonionemus.

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