MUSEUM OF COMPAKATIVK ZOOLOGY. 91 



It is unquestionably to the presence of this highly developed vascular 

 network that the pink color of the living fishes is due ; and it is un- 

 doubtedly by this, in part, but mostly by the much thickened sub- 

 epithelial connective tissue, that the pigment is disguised in the 

 preserved specimens.^ 



And now as to the reason for this highly vascular condition of the 

 skin, which is certainly unusual, as I have convinced myself by exam- 

 ining the integument of several other bony fishes, both by sections and 

 by the same methods of treatment that were used in prepai'ing the 

 specimens shown in Figures 4 and 11. 



I will consider the sevei-al explanations that have suggested them- 

 selves, in the order in which they have occurred to me. 



When I first saw the living specimens, T supposed their pink color to 

 be due to the fact that the pigment had disappeared from the skin on 

 account of the constant darkness in which the fishes live ; and that, it 

 having thus become somewhat translucent, no scales whatever being 

 present, whatever of vascularity there might be in the tissues of the 

 body wall became visible through the integument. This explanation 

 lost all its force, of course, as soon as it was noticed that the pigment 

 is present in large as well as in small specimens, and that the blood- 

 vessels are situated between the pigment layer and the epidermis, and 

 not under the former. I would not be understood to mean by this that 

 the pigment layer is so dense that it would much obscure the vascular- 

 layer were it superficial to the latter. 



The next hypothesis that presented itself to me was suggested by the 

 fact mentioned by Dr. Eigenmann, that the crustacean with which the 

 fishes so constantly live is also of the same pink color. Have we here 

 a case of protective resemblance 1 An entirely satisfactory answer to 

 this question cannot be given until we know mure of the habits of the ' 

 fish in its native conditions of life, and also of the structure and habits 

 of tlie crustacean in company with which it lives. So far, however, as 

 our present knowledge enables us to see, there are some quite serious 

 obstacles in tlie way of this supposition. It is probable that the fish 



1 I may add, that on examining several large specimens preserved in alcohol 

 exclusively, I find that the pigment is very distinctly seen on the whole dorsal 

 surface, without removing the skin. As the epidermis in these specimens is 

 quite loose as compared with that of specimens preserved in picro-nitric, picro- 

 sulphuric, or Perenyi's fluid, I explain the greater distinctness of the pigment 

 by supposing that in the alcoholic specimens the sub-epithelial connective tissue 

 has shrunken more by dehydration than it has in the other methods of fixation, 

 and also more than has the epidermis. 



