Significance of Coiispiciiousness in C oral-Reef Fishes. 311 



selection so far as concerns the color characters of the fish. Selection has 

 neither produced nor perfected the color characters ; they have, on the con- 

 trary, arisen in the absence of selection and may be regarded as expressions 

 of the individuality of the species unhampered by selection as expressions 

 of the action of internal factors, possibly orthogenetic. 



In the reef environment the chemical composition, temperature, and 

 illumination of the water show a high degree of uniformity both sea- 

 sonal and regional (Hickson, quoted by Packard, 1902). In this environ- 

 ment many of the fishes that live habitually in the reefs are highly conspicu- 

 ous on account of their coloration or other characters, while other fishes 

 that live habitually about the reefs but not in them are inconspicuous. Con- 

 spicuous coloration can not, then, be attributed to the influence of light, 

 temperature, or chemical composition of the water, which are the same in the 

 reefs and about them (Hickson). Possibly the food of the reef fishes or un- 

 known external factors tend to stimulate in them the development of a bril- 

 liant coloration, and this might be experimentally tested. That the environ- 

 mental factors peculiar to the reefs do not necessarily produce such colora- 

 rion is shown by Kyphosiis sectatrix, a reef-fish in the stomach of which 

 Linton (1905) found crabs, lamellibranchs, and vegetable debris. This fish 

 is dull-colored and inconspicuous, yet is found with the conspicuous fish and 

 lias like food. But even should it be shown that the reef environment in- 

 cludes factors which tend to produce brilliant colors the many color-patterns 

 characteristic of species would remain unexplained ; for the number of color- 

 patterns among coral-reef fish is very great, while the environment is one of 

 great uniformity and the food of the species is little varied.^ The character- 

 istic colors and patterns I can regard only as due to internal factors, unchecked 

 by the selection which renders them impossible in the immediate neighbor- 

 hood of the reefs. The reef fauna may include fish conspicuous or not, 

 according to their nature ; the water immediately about the reefs can harbor 

 only relatively inconspicuous fish. Nor does it seem to me possible that 

 reef fish could have developed conspicuousness outside the reefs and then 

 sought their shelter (Davenport, 1903, segregation in the fittest environ- 

 ment), for conspicuousness at a distance from the reef shelter would be fatal. 

 On the other hand, inconspicuous fish may have appeared in the reefs and 

 then made their way out from them. Coral-reef fishes are not conspicuous 

 because they are in the reefs; they are in the reefs because they are con- 

 spicuous and can not therefore leave the reefs, and because, being in the 

 reefs and taking the food as they do, there is no reason for their being incon- 

 spicuous. The reefs condition their conspicuousness; they are in no sense 

 its cause. 



'The conditions resemble those found by Gulick (1905) in the Hawaiian Achatinel- 

 lidse, but as my own observations are insufficient to warrant the discussion of divergent 

 evolution, I do not here consider Gulick's work. 



