NATURAL HISTORY OF AMERICAN LOBSTER. 193 
Soon after the water has been brought to the boiling point the red color becomes 
permanent. 
The colors of deep-sea animals that live in total obscurity can not be of any utility 
to the animal as a source of protection. The color may be very brilliant, red, scarlet, 
orange, rose color, purple, violet, and blue, which is less frequently reported, but they appear 
to be developed quite independently of the light. It has been shown by experiment 
with sensitive photographic plates that luminous rays do not penetrate ordinary sea water 
to a greater depth than 400 meters, as noted above. In depths of 50 fathoms or more 
there might be an appreciable amount of light on clear days, but even then, when the water 
was loaded with sediment and the bottom composed of dark materials, it seems hardly 
probable that colors would have any protective value whatever. 
The normal colors of the lobster, which are spread like a mantle over the whole 
upper surface, tend undoubtedly to obliterate it and to screen its movements while 
crawling over a weedy or rocky bottom. The absence of all color or a more generous 
display of bright pigment would make it a more conspicuous object, especially upon 
sandy bottoms in shallow water, which it is usually careful to avoid in the daytime. 
The vivid red of the claws appears to be overlaid by a darker pigment in spots, particu- 
larly on the upper surface. The underside of the pleon, which rests upon the bottom 
when the tail is not folded, is very meagerly supplied with pigment, as is usually the case 
with marine animals which inhabit the bottom. 
48299° — Bull. 29 — 11 13 
