ZOOLOGY: W. J, CROZIER 
673 
ation is always conspicuous, not only because of its brilliancy but also 
by reason of the freedom with which they expose themselves in bright 
sunlight upon bare open bottoms or (a favorite situation) on eel grass 
in tidal 'creeks/ The animals are positively photo tropic. Their con- 
spicuousness is entirely independent of their being viewed form above 
the water surface. 
Less than two per cent of the specimens collected are found to show 
evidence of mutilation. As these nudibranchs regenerate very slowly 
(Child, and my own observations), this evidence is significant. 
Experiments in feeding entire, undamaged specimens of this nudi- 
branch to other animals, both in natural surroundings and under favor- 
able conditions in aquaria, have shown that to all the animals usually 
associated with Chromodoris its flesh is repugnant. This is true of 
fishes as well as invertebrates, including anemones, Crustacea, various 
worms, and starfish. Some fishes which feed by night (squirrel fishes), 
and others which hunt their prey by sight (snappers), will make several 
attempts to bite a Chromodoris when it is first dropped into their aqua- 
rium tank, but thereafter will not approach it; after the nudibranch 
has sunk to the bottom and begun its normal creeping, it is never seri- 
ously molested. 
The unpleasant quality is associated with the skin, since the internal 
organs are greedily devoured. The blue pigment is not the unpleasant 
substance, for the intensely blue rhinophores are eaten readily, while 
the blood, which I have elsewhere shown to contain the blue skin pig- 
ment (presumably as a respiratory chromogen of some sort), evokes 
positive food-taking responses from various fishes, crabs, and anemones. 
The yellow pigment is not the responsible agent, as it is absent from 
the edge of the mantle, a region which comparative tests indicate to 
be the most 'unpleasant' part of the animal's body. 
Small pieces of the skin of Chromodoris will be snapped at several 
times by a fish (over twenty species have been tested), while an intact 
nudibranch will usually be merely approached, 'nosed,' and perhaps 
bitten once, if the fish swims up suddenly, before it is left alone. The 
explanation of this behavior is found in the fact that when the intact 
nudibranch is locally disturbed by being handled severely, bitten, cut, 
stung by nematocysts, or stimulated with induction shocks, it excretes 
from the irritated area, into the sea water, a bluish-white material 
which causes immediate negative reactions in fishes and in all classes 
of marine invertebrates which I have tested. Isolated portions of the 
Chromodoris skin, however, give the reaction with difficulty, if at all, 
and then only to a slight extent. 
