OCTOBEK 6, 1911 J 



SCIENCE 



453 



tween 29 and 250 fathoms. The association 

 of species of the two genera may be more ap- 

 parent than real, for the species of Cyclogaster 

 are typically bottom-inhabiting forms and 

 those of Careproctus free-swimming. The 

 distribution of the light-colored and black 

 forms overlap between 400 and 1,000 fathoms. 

 The gradual merging of one environment into 

 another and the force of heredity may account 

 for the overlapping of the faunas, but, as is 

 the case with the shallow-water species, the 

 differently colored ones may not intermingle. 

 Let us imagine a portion of the ocean bottom 

 as illuminated by a lantern. A black fish on 

 a. dark bottom or near the margin of the illu- 

 minated area would be practically invisible. 

 A transparent or a reddish translucent fish 

 would be little more discernible. Away from 

 the bottom and near the source of light a 

 black fish would be more conspicuous than 

 the others. At such depths it is difficult to 

 decide which species rest upon the bottom and 

 which swim freely some distance above it. 

 The deep-sea Cyclogasterids, which, from their 

 structure, we assume to be free-swimming, are 

 nearly all light-colored. Nearly all of those 

 which appear to live upon the bottom are 

 black. It should be noted that among other 

 deep-sea fishes a number of free-swimming 

 species are black and also that some of the 

 bottom-inhabiting species may be light-col- 

 ored. It can be seen from the above discus- 

 sion that the light-colored species in the 

 depths below the penetration of sunlight may 

 be as protectively colored as the black forms. 

 The disparity in the numbers of light-colored 

 and black species suggests that this is not 

 true or that the majority of the species live 

 upon or very close to the bottom. 



The significance of the predominance of 

 reddish color in the light-colored species is 

 unknown. This type of coloration may be 

 considered as being intermediate between the 

 translucent and black types and having the 

 partial advantages of both. In dealing with 

 this question the color perception of the eyes 

 of fishes should be taken into consideration. 

 If the eyes of fishes lack the color perception 

 of our own and are sinaply camera eyes the 



reddish species will appear gray and be incon- 

 spicuous in their environment. 



We have intimated that, in addition to a 

 change in coloration, the deep-water species 

 become translucent. The tide-pool species are 

 soft and flabby and no great change is re- 

 quired for them to assume a translucent jelly- 

 like appearance. 



In concluding I wish to express my appre- 

 ciation of the work of the Michael Sars in 

 1910. The observation made on this expedi- 

 tion that the coloration and bathymetrical 

 distribution of the young fishes are correlated 

 from the earliest stages is confirmed by my 

 work on the Cyclogasteridse. The young of 

 these fishes inhabit the same regions as the 

 adults and are similarly colored. Dr. Hjort's 

 suggestion that the 500-meter or 273-fathom 

 level marks the border between two diflerently 

 colored faunas does not harmonize with the 

 conclusions I have reached from a study of 

 the CyclogasteridsB. The acquisition of more 

 carefully taken records of these fishes result- 

 ing from expeditions as carefully planned as 

 that of the Michael 8ars may cause us to 

 modify our conclusions concerning the impor- 

 tance of the 273-fathom level in relation to 

 the distribution and coloration of the Cyclo- 

 gasteridse and bring them more in accord with 

 those of Dr. Hjort. 



Charles Victor Burke 



Falo Alto, Cal. 



SPECIAL ABTICLES 



ISOSTASY, OCEANIC PRECIPITATION AND THE 

 FORMATION OF MOUNTAIN SYSTEMS 



The theory of isostasy postulates the uni- 

 formity of the weight of the earth's crust over 

 the surface of the earth. It was suggested 

 by Major Sutton* in 1889. It has recently 

 received considerable attention by geodesists 

 and geologists and has received quantitative 

 confirmation by the researches of Hayford." 

 Eeeent work has been along the line of in- 

 vestigating the effect of displacement by 

 erosion and the resulting equilibrium flow. 



''Bull. Phil. Soc. Washington, 11: 51-64, 1889. 



= See Science, February 10, 1911; also H. F. 

 Reid, Proc. Am. Phil. Soc, 50: 444-^51, 1911. 



