POPULAR SCIENCE MONTHLY 



THE STRUCTURE OF BLIND FISHES. 



By GAEL JL EIGENMANN, 



PROFESSOR OF ZOOLOGY, INDIANA UNIVERSITY. 



r I ^HE Color of the Amblyopsid-e. — The three species of Cholo- 

 -L gaster are colored, with varying intensity, from C. cornutus, 

 which is darkest, to C. Agassizii, in which the color is faintest. The 

 color cells are in all cases arranged in a definite pattern. These 

 are determined by the underlying muscles. The pattern consists 

 of three longitudinal bands on the sides, following the line where 

 the muscle segments are angularly bent, and cross-stripes along 

 the line separating successive segments. 



The general color of Typhlichthys is cream and pink. It is 

 abundantly pigmented. In younger specimens the pigment is 

 arranged in more definite areas about the head. In the old it 

 is more uniformly distributed, being, however, specially abund- 

 ant about the brain. The pigment pattern of the body is pre- 

 cisely as in Chologaster, except that the individual pigment 

 cells are minute and their aggregate not evident except under 

 the lens. 



The retention of the color pattern of Chologaster in Typhlich- 

 thys is not less interesting than the retention of similar habits. 

 It is perhaps due to different causes. The color pattern in Cholo- 

 gaster is determined by the underlying muscular structure, and 

 the retention of a similar pattern in Typhlichthys is due to the same 

 underlying structure, rather than to the direct hereditary trans- 

 mission of the color pattern. 



Amblyopsis is flesh-colored, ranging to purple in the gill region, 

 where the blood of the gills shows through the overlying struc- 

 tures, and over the liver, which can be seen through the translu- 

 cent sides and ventral wall. About the head and bases of the fins 

 the color is yellowish, resembling diluted blood. The surface of 

 the body is slightly iridescent, and the surface of the head has a 

 velvety, peach-bloom appearance. 



The general pink color of Amblyopsis is due to the blood. 

 It is not due to any abnormal development of blood-vessels in the 

 dermis. In the fins, where the blood-vessels are near the surface, 

 the general effect is a yellowish color. The surface vessels of the 

 dermis also appear yellowish. It is only on account of the trans- 

 lucent condition of all the tissues, permitting the deeper vessels 

 to show through a certain thickness, that the pink effect is pro- 

 duced. Amblyopsis has always been spoken of as white. The 

 term " white aquatic ghosts " of Cope is very apt, for they do 



