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'’! 
Sarsia and Tiaropsis (Hydromedus) 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’ ‘iaropsis 
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. Sarsie 
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 
(Scyphomeduse) meduse, 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. 
