MUSEUM OF COMPARATIVE 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 preparing the 
specimens shown in Figures 4 and 11. 
I will consider the several explanations that have suggested them- 
selves, in the order in which they have occurred to me. 
When I first saw the living specimens, I 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? An entirely satisfactory answer to 
this question cannot be given until we know more of the habits of the 
fish in its native conditions of life, and also of the structure and habits 
of the 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 the 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 hoy! in the other methods of fixation, 
and also more than has the epidermis. 
