ADJUSTMENT OF FLATFISHES 415 



Especial mention must here be made of one spot, differing in 

 some respects from the foregoing, and lying just behind the base 

 of the pectoral fin. This spot is elliptical in shape, and bounded 

 by a paler outline, in which the dots are commonly not very 

 distinct. It undergoes great and oftentimes very rapid changes 

 of shade, and is frequently the most conspicuous white spot 

 upon the fish. Under certain conditions of extreme contrast in 

 the skin pattern, this spot isJound to merge into adjacent white 

 areas, so as to form an irregular white blotch of considerable size 

 (figs. Ij, H, etc.). 



2. Small, nearly circular spots, more regular in outline than 

 those of the preceding type, and in some respects just the reverse 

 of the last. Each consists of a dark ring, inclosing a center which 

 is usually somewhat paler than itself, and the spot as a whole is 

 usually somewhat darker than the ground-color of the fish. These 

 spots are generally much less conspicuous than are the pale spots, 

 and at times they practically disappear from view. At other times, 

 however, they stand out as dark brown circles against a paler 

 background (figs. 2c, 3a). It is probable that these spots, like 

 those first considered, are fairly constant in their arrangement 

 for all members of the species. 



3. Large dark blotches of variable occurrence, which may 

 better be characterized as 'permanent possibilities' than as con- 

 stant features of the pigment pattern of the fish. These large 

 blotches appear, in every case, to form around one of the 

 spots of the preceding type (2) as a nucleus. They are conspicu- 

 ous features of the skin pattern, in all cases where a blotched or 

 highly contrasted appearance is exhibited, and it is probable 

 that they always reappear in the same positions. On the other 

 hand, they may be wholly wanting when the animal assumes a 

 homogeneous or fine-grained appearance. The most nearly per- 

 manent blotches of this type are three which occur along the lateral 

 line. The second of these, lying about two thirds of the dis- 

 tance from the snout to the base of the caudal fin, is the most 

 constant of the three, and in some specimens probably never 

 wholly disappears, even when the fish is in the most extreme con- 



