6 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



the animals changed, some coming to the surface and others going 

 to the bottom. 



These experiments show beyond doubt that Charybdea is sensitive 

 to light, and that it is moderate light that stimulates the animals to 

 activity, while darkness and strong light inhibit activity. While the 

 individual exceptions, as Conant himself suggests, are well explained 

 on the supposition of individual diversity, yet it appears that other 

 conditions, such as the time of day, temperature, etc., may have been 

 responsible for some of the exceptional experiments in which no 

 animals responded as expected. 



While light of any intensity seems to have stimulated Romanes 11 

 Sarsia and Tiaropsis (HydromedusaB) to activity, we note that it 

 is moderate light that stimulates Charybdea. This fact is evidently 

 correlated with the circumstance that Charybdea usually lives upon 

 or near the bottom. 



It may further be added in regard to Romanes 1 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. Sarsiae 

 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 

 (Scyphomedus*) medusa, 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 swim- 

 ming 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", who further states that this medusa may be deceived 

 into laying its eggs by placing it in the dark. 



