92 BULLETIN OF THE 



has adopted its present mode of life as a means of escape from its ene- 

 mies, so that protective coloration could be of no use, and consequently 

 natural selection would have no power to establish the color. 



It is true that there are recorded a few cases of animals that are 

 apparently protectively colored, which at the same time depend upon 

 concealment to escape their enemies ; e. g. the caterpillar of the moth 

 Mania typica (A. R. Wallace, '89). But these are certainly very ex- 

 ceptional ; and if the law of natural selection is to be held as applying 

 to them at all, we are compelled to assume that either the coloration 

 must have been produced in some other way than through it, or that 

 neither the color protection nor the concealment is adequate in itself 

 to effect the degree of protection necessary for the preservation of the 

 species. On this supposition, it is possible that natural selection has 

 been operative in producing the color ; but Dr. Eigenmann ('90, p. 68) 

 tells us that Typhlogobius " never leaves its subterranean abode"; and 

 the extent to which the eyes are reduced affords very strong proof in 

 confirmation of this statement. Again, on physiological grounds, it 

 would seem that had the color been produced for the mere purpose of 

 the color alone, it would have been effected by a deposition of pig- 

 ment, and not by such an enormous increase in the quantity of blood- 

 vessels and blood ; for certainly the former would have been more 

 economical. 



And this brings me to what I believe to be the true explanation of 

 the condition. I believe it to be for the purpose of cutaneous respira- 

 tion. Says Prof. N. Zuntz ('82, p. 114): "Wo auch immer das Blut 

 mit der Atmosphare oder mit gashaltigem Wasser in Contact kommt, 

 muss, in derselben Weise wie in der Lunge, ein auf Ausgleich etwaiger 

 Spannungsanderungen hinzielender Diffusionsstrom der Gase auftreten." 

 The conditions for such a diffusion seem to be present here. That 

 cutaneous respiration takes place as a normal process in many vertebrates, 

 both terrestrial and aquatic, is generally admitted by physiologists.* For 

 the present purpose I need only to consider in some detail what is known 

 about the process in some of the aquatic forms. 



Spallanzani (1803, pp. 71, 114) was the first to show that the frog by 

 means of respiration through the skin continues to live for a long time 

 in air after the extirpation of the lungs. W. F. Edwards ('24, pp. 41- 

 62) confirmed Spallanzani's results, and added the observation that this 



1 For a discussion of this question, see the larger works on physiology, and par- 

 ticularly Milne-Edwards, '57, pp. 632-635, and Hermann, '82, pp. 114-117. 



