672 
ZOOLOGY: W. J. CROZIER 
6. Finally in problems of thermodynamics, there would seem to be no 
valid objection to its use. In the characteristic equation for a pure 
gas, the product of the new reading and the gas constant give as be- 
fore a measure of the kinetic energy of translation of the molecules. 
Similarly in Avogardo's law, we have an even more definite conception 
of the temperature function; and also in the Stefan-Boltzmann law of 
black body radiation. 
ON THE IMMUNITY COLORATION OF SOME NUDIBRANCHS 
By W. J. Crozier 
BERMUDA BIOLOGICAL STATION FOR RESEARCH, AGAR'S ISLAND, BERMUDA* 
Read before the Academy, November 14. 1916. Received. November 8, 1916 
Certain large nudibranchs, notably species of ChromodoriSy exhibit 
a combination of brilliancy of pigment pattern and boldness of habits 
sharply distinguishing them from related nudibranchs which appear 
to be efficiently protected by their concealing coloration and behavior. 
It has long been suspected that the strikingly colored chromodorids 
achieve an immunity from predatory enemies by virtue of some dis- 
tasteful quality, according to the classical conception of 'warning color- 
ation.' The experimental evidence for this belief, as presented by 
Herdman and by Crossland, has remained, however, very fragmentary 
and is indeed far from carrying conviction. 
For several years I have been interested in the pigmentation of the 
large Bermudian Chromodoris zebra Heilprin, mainly because its blue 
integimientary pigment is available as an intracellular indicator of 
acidity. On the basis of field observations, continuous throughout the 
year, I was led to undertake a series of experiments intended to throw 
light upon the possible biological meaning of this animal's coloration. 
The outcome seems reasonably conclusive, and it leads to the rejection 
of the idea that a warning significance attaches to the pigmentation 
of Chromodoris. By inference, one is inclined to suspect that more com- 
plete study will reveal analogous conditions with reference to other 
brightly colored nudibranchs. 
The pigment pattern of C. zebra is, in brief, an irregular streaking of 
yellow or orange upon a field of blue. The foot, the ventral surface 
of the mantle, and various less conspicuous parts are of a pure blue. 
The animals occur at various stations, ranging in depth from about 
10 fathoms to the surface of the water. They are most abundant, 
though, in quite shallow water, except during a portion of the summer 
and immediately after severe storms at other seasons. Their color- 
*Contributions from the Bermuda Biological Station for Research, No. 51. 
