THE COLOEATION OF REEF FISHES 573 



it appears that either would be more conspicuous than the 

 other, if displayed in its stead. But the extreme phases of 

 coloration are not essentially different from the intermediate 

 ones, and may be separated in time by no more than five 

 seconds, and, in space, by as many feet. Is the dark fish under 

 the head less immune from attack than when it is a yard from 

 shelter, that it should assume a more conspicuous pattern as it 

 moves from beneath it? Or is this contrastive design in brown 

 and gray a warning combination, whose serviceableness dimin- 

 ishes as the fish moves still farther into the open? It seems 

 impossible to answer such questions in the affirmative; yet, if 

 all are aspects of obliterative coloration, no combination of 

 brown and gray that may appear upon the reef fishes in an 

 unchangeable pattern may be assigned to another category, un- 

 til it is proven that its possessor's normal range lies beyond the 

 bounds within which the changeable forms show comparable 

 phases. 



Yellow is not of common occurrence in large patches upon the 

 reefs, so it is virtually impossible to make extended observations 

 upon its effect in evoking yellow phases, which, by the way, are 

 not frequently encountered among the fishes, in spite of the fact 

 that yellow marks or washes appear in abundance. 



The red parrot fish (S. abildgaardi), with its notable power of 

 color change and capacity of adjustment to light and dark back- 

 grounds, in its darkest phase is distinctly washed with yellow 

 over the whole top of its head. The immature blue-head (T. 

 bifasciatus) has a gray phase with no yellow, assumed over 

 sand, and a yellow phase which it resumes when it returns to 

 more variegated surroundings. There are also indications that 

 the porgy (Calamus arctifrons) dons and doffs its yellow with 

 reference to the character of the underlying bottom. Thus yel- 

 low may occur in combination mth brown and gray, colors to 

 which no conspicuousness attaches in themselves. In some 

 species it is suppressed, when its bearer passes into an environ- 

 ment to which the color is foreign, and reappears only upon its 

 departure from that place Hence in its bionomic relations it 

 seems to differ in no wise from the colors already considered. 



