142 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



length. When captured by the fishermen they are usually of a rose or delicate lilac 

 color, but lose these tints or become of a light-yellowish hue when kept in vases with 

 white bottoms. In black vases they turn to a deep brown. These effects are produced 

 by the reaction of two kinds of pigments, the cyanic pigments which are generally in 

 a state of solution, and the pigments of the xanthic series (red, orange, and yellow), 

 by the action of the chromatoblasts. Malard states that Jourdain has shown that if 

 the eyes are removed and the animal is kept in darkness, a red color is always obtained. 



Certainly, one of the most striking cases of protective coloring met with in the 

 Crustacea is that of the inhabitants of the floating islands of sargassum which are 

 encountered in the Gulf Stream or along its borders. This alga is of a dirty yellowish- 

 brown color, often flecked with white, when its floats are incrusted with the bleached 

 skeletons of bryozoa. This appearance is emphasized by the numbers of goose bar- 

 nacles which are attached to the fronds. A small crab which is an important colonist 

 of these islands is brown, with a large snow-white spot on its back; and the shrimp, 

 of which there are several species, are colored in a similar manner, the body being 

 dappled with brown and white. 



We must place m another category the gaily dressed shore crab of the West Indies, 

 Gegarcinus ruricola, whose brilliant hues and bizarre coloration are clearly without 

 protective significance. This beautiful crab burrows in the mangrove swamps at about 

 the level of high water, and is very common throughout the Bahama Islands. After 

 a drenching rain the green boughs of the mangrove suddenly blossom out with crabs. 

 Some of them have crimson legs, a dark purple body, with a large yellow spot on each 

 side of the carapace, while iu others these colors are reversed. Others again are 

 nearly black, or the carapace is orange or straw color, flecked or marbled with purple, 

 in an endless series of patterns, so that no two are alike. It is possible that this is 

 an example of warning coloration, such as is seen in mauy gaudy insects, serving to 

 protect them from the assaults of birds and other enemies, or it may be a case of 

 substantive variation, without any vital significance. 



The colors of deep-sea animals which live in total obscurity can not be of any 

 utility to the animal as a source of protection. The colors may be very brilliant — red, 

 scarlet, orange, rose color, purple, violet, and blue being 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. 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 its whole 

 upper surface, tend undoubtedly 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, particularly on the 

 upper surface. The under side 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. 



