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SCIENCE 



[N. S. Vol. XXXIV. No. 875 



distribution. The question naturally arises: 

 are these fishes protectively colored, or, is the 

 color dependent upon the modification of 

 structure or some other factor besides the 

 color of the environment? The question is 

 complex, because there is a parallel modifica- 

 tion of color and structure due to the environ- 

 ment of the deep sea. It frequently happens 

 that a certain type of structure is associated 

 with a certain type of coloration. Also the 

 coloration of the species sometimes appears 

 to be independent of either the color of the 

 environment or the type of structure. Those 

 biologists who view with suspicion the at- 

 tempts to explain the coloration of tide-pool 

 fishes by means of the protective coloration 

 theory will be even more skeptical toward any 

 effort to explain the coloration of deep-sea 

 fishes by means of the same theory. The fac- 

 tors of a tide-pool environment are spread out 

 before us but those of the deep-sea are hidden. 

 We do not know that there is sufficient light 

 in the greater depths of the ocean to enable 

 the fishes to see and of course without light 

 there can be no protective coloration. If this 

 is a region of total darkness the color of an 

 animal can not be an aid to its concealment. 

 So far as protection is concerned a fish may 

 just as well be brilliantly colored as trans- 

 parent or black. But they are not brilliantly 

 colored. Instead they are typically of a uni- 

 form coloration, which is usually black. In 

 the regions of dim light they are of another 

 color. The coloration bears some relation to 

 the depth at which the species exist. The 

 amount of sunlight depends upon the depth 

 and consequently the coloration appears to 

 depend upon the amount of sunlight to which 

 the species are subjected. There are two pos- 

 sible sources of light in the oceanic depths 

 below the penetration of sunlight. We know 

 that certain animals of this region have light- 

 producing organs and the decomposing ani- 

 mal matter may give forth a phosphorescent 

 glow. And, as if for the purpose of sight in 

 a dim light, the eyes of the fishes have become 

 greatly enlarged. Regardless of the merits 

 of the protective coloration theory it furnishes 

 us with a fascinating field for speculating. 



The attempt to explain some of the facts con- 

 cerning the coloration of the Cyelogasteridae 

 by the protective coloration theory will not be 

 amiss here. 



The environment of the deep sea has had a 

 different effect than the dark cave environ- 

 ment upon fish life. Dr. Eigenmann has made 

 an exhaustive study of cave fishes. In these 

 fishes the eyes atrophy and the pigment is 

 reduced or absent. Dr. Eigenmann believes 

 that we have here an example of the inherit- 

 ance of an acquired characteristic. The case, 

 as he so ably presents it, appears unassailable. 

 The color of some of the cave fishes can not be 

 protective, for there are no enemies to protect 

 them from. The fishes of the deep sea are 

 surrounded by other fishes with large eyes and 

 long teeth. The presence of a light would 

 allow the struggle for existence to become 

 more intense. The effects of a cave environ- 

 ment and the deep-sea environment upon the 

 coloration of fishes are similar up to a certain 

 point and then widely diverge. The effects 

 of the dimly lighted cave and the dimly 

 lighted regions of the ocean lead to the reduc- 

 tion of pigment. The effect of a totally dark 

 cave is to allow the fishes to lose all their 

 pigment. In contrast to this the fishes in the 

 ocean below the penetration of sunlight ac- 

 quire pigment and become wholly black. 

 Possibly the difference in the effects of the 

 two environments can be explained by the 

 protective coloration theory, which can not 

 explain the coloration of cave animals but may 

 explain the coloration of deep-sea animals. 



The overlapping of faunas calls for further 

 discussion if we are to consider the fishes as 

 protectively colored. The genus Careproctus 

 originated in moderately deep waters. From 

 this region representatives of the genus mi- 

 grated into shallower waters and down to great 

 depths. Those that entered shallower waters 

 retained their light and uniform coloration. 

 Of those that descended to greater depths 

 some retained their original coloration, but 

 the majority became black. The species that 

 entered shallow water became associated with 

 the variegated species of Oyclogaster. The 

 distribution of these two genera overlap be- 



