Chapter VIII.— VARIATIONS IN COLOR. 



In the study of the color of animals we must distinguish between (a) variations in 

 colors themselves and (b) variations in color patterns. The variation in colors, which 

 Bateson calls "substantive variation," may be the result of a physical or chemical 

 change and has no vital significance, like the change of yellow phosphorus to the red 

 variety, of blue to red litmus, or of green to red pigments in autumn leaves and in the 

 shell of the living lobster when the latter is boiled. " Different colors," says Bateson, 1 

 "are liable to different discontinuous variations; as instances may be mentioned black 

 and tan in dogs, olive brown or green and yellow in birds, red and blue in the eggs of 

 many Oopepoda," etc. "Discontinuous color variation of this kind is one of the com- 

 monest phenomena in nature." The dark green and golden yellow in the eggs of several 

 species of Alpheus and many other macrura is a characteristic example (94). Such 

 changes can have no protective or adaptive significance. 



The color of the lobster 2 is primarily due to the presence of pigments, either in 

 solution in the blood or in the form of granules in the protoplasm of certain cells, 

 particularly the chromatoblasts, which lie beneath the cuticular epithelium The 

 chromatoblasts are richly supplied with blood, which flows in a system of irregular 

 sinuses through the spongy tissues underlying the epidermis. 



In the adult lobster the shell is an opaque, dead substance, and the pigments 

 which give it color are excreted by the chromatoblasts lying in the soft skin which is 

 exposed upon removing the shell. This skin is flecked and mottled with scarlet, and 

 it takes only a simple magnifying glass to see that its color is due to the branching 

 pigment cells, accumulations of which correspond to the blotches of pigment on the 

 shell. The excreted pigments undergo physical and probably chemical changes in the 

 shell, and become of a very different color from that of the chromatoblasts. 



Since the colors of the adult lobster reside in a dead body — the pigment layer of 

 the shell (see pp. 77-78) — it is evident that no changes of a vital nature can take place 

 after this is definitively formed. A young male, 10 inches long, drawn and colored from 

 life, is represented on plate 16, fig. 22. This may be taken to represent the average 

 color in lobsters with moderately hard shells. 



NORMAL COLORATION. 



There is no apparent sexual variation in the color of the lobster. The following 

 detailed description is drawn from a female 10§ inches long, with elastic or " buckle" 

 shell and with nearly ripe ovaries. 



The general cast of color of the upper parts is dark bluish-green, mottled and 

 speckled with very dark greenish- black spots; tail-fan light greenish-olive; sides of 

 carapace brownish-olive, conspicuously spotted with small greenish-black spots; sides 

 of abdomen marked in the same way, spots not as numerous; no spots on upper 

 surface of uropods; large chela; above dark bluish-green, almost black, with suffusions 

 of orange on propodus; tubercles and spines bright red; spiues of rostrum, antennae, 



1 Materials for the study of variation, treated with especial regard to discontinuity in the origin 

 of species, by William Bateson. 1894. 



2 The color variations in the young are discussed on p. 184. 



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