416 FRANCIS B. SUMNER 



dition of pallor. But it is likely that dark areas may form on 

 occasions around any of the spots of the second type. 



4, As a phenomenon parallel to that last mentioned, the intra- 

 annular areas seem at times to overflow their boundaries, thus 

 producing larger pale blotches (figs. 11, 4d). This fact has already 

 been pointed out in speaking of the elliptical pale spot behind the 

 pectoral fin. 



There remain still more vague an.d impermanent arrangements 

 of the pigment, which are very difficult to describe. Moreover, 

 aside from these various types of spots and blotches, the remain- 

 der of the skin surface does not present a homogeneous coloration, 

 but exhibits at times more or less well defined areas differing from 

 one another in shade. Frequently, too, the outlines of the scales 

 are conspicuously visible, contributing materially to the 'grain' 

 of the surface. 



Allowance must, of course, be made for the superficial character 

 of the foregoing description. This crude classification of the 

 markings of the fish is based upon external appearances only, no 

 histological study of the skin having been undertaken. Indeed, it 

 is probable that much of the diversity in the distribution of visible 

 pigment in the skin of Rhomboidichthys is ''functional" rather than 

 "organic." Or, better stated, it may result not so much from diver- 

 sity in the distribution of the chromatophores, as from local 

 differences in their tonus, under the influence of the nervous 

 system, these last being determined perhaps by the distribution 

 of the efferent nerve fibers. '^ 



Regarding the color of Rhomboidichthys, little need be said at 

 present, since this will be discussed in relation to the various phases 

 assumed by the fish. I need only state here that the animal is 

 almost wholly restricted to black, white and various shades of 

 gray, brown and yellow. It must be added, furthermore, that the 

 browns and yellows are scarcely ever brilliant in quality, being 

 dull tones, of a low degree of saturation. Thus they depart little, 

 if at all, from the various hues which we encounter among the 



^^ Mayerhofer (Archiv fiir Entwicklungsmechanik der Organismen, 1909) 

 states that the chromatophores of the pike {Esox lucius) are distributed uniformly 

 without reference to the dark crossbands of the body. 



