798 THE AMERICAN NATURALIST.  [VOL. XXXIII. 
It is somewhat unfortunate for this argument that few if 
any of the fixed Coelenterata that are remarkable for their 
phosphorescence possess nematocysts that are likely to be 
regarded by a hungry fish as at all formidable. The Gor- 
gonidz, Antipathidz, Alcyonidz, and Pennatulidz, all notably 
phosphorescent, are almost if not quite destitute of nematocysts. 
- As for the Hydroida, there is only one known species, so far 
as I can learn, whose nematocysts can be felt at all by the 
human skin. Millepora, if it be a hydroid, is of course another 
exception. 
Neither is it likely that the phosphorescence of these fixed 
forms serves the same purpose as attractive coloration. Al- 
though the Ccelenterata are, in general, bisexual, the sperma- 
tozoa are shed into the water to find their way as best they can 
to the female element in other colonies. So far as I know, the 
colonies of both sexes are phosphorescent, but the light, in the 
hydroids at least, seems to be mainly confined to the polyps, or 
nonsexual ‘‘ persons,” excepting in those forms that produce 
medusz. 
Having shown that the phosphorescence of fixed forms can- 
not be regarded as protective, and that it does not appear to be 
for the purpose of attracting or guiding the sexes in coming 
together, we turn to a third and more promising explanation. 
The food of the fixed Coelenterata consists mainly of either 
Crustacea of the smaller sorts, their embryos, the Protozoa, or 
the unicellular plants, such as diatoms. 
Most of the minute Crustacea have effective eyes, and it has 
been repeatedly demonstrated that they are attracted by light, 
both artificial and natural. Crustacean embryos usually have 
eyes that are very large in proportion. In many cases these, 
too, are attracted by light. Although I know of no direct 
experiments being made with phosphorescent light, it is reason- 
able to suppose that it would affect them in a like manner, 
although probably in a less degree. If this is true, the phos- 
phorescent powers of the fixed Coelenterata would cause the 
small crustaceans, and more surely their embryos, to congregate 
near the illuminated areas, and thus be captured. This is on 
the same principle that many fishes, birds, and even mammals 
