THE STRUCTURE OF BLIND FISHES. 49 



appear white in the caves, and their gliding motion has an uncanny 

 effect. All alcoholic specimens are white. 



The pigment cells can not be made to show themselves, even 

 by a prolonged stay in the light. The old, if kept in the light, will 

 not become darker, and a young one reared in the light until ten 

 months old not only showed no increase in the pigmentation but 

 lost the pigment it had at birth, taking on the exact pigmentless 

 coloration of the adult. Pigment cells are late in appearing in 

 Amblyopsis. When the young are two months old pigment is 

 abundant. This pigmented condition is evidently a hereditarily 



Fig. l. — C/iologuster Agassizii from Cedar Sinks Cave, Kentucky. 



transmitted condition. It disappears with age. Primarily this dis- 

 appearance was probably individual. But, 'as in the flounder, the 

 depigmentation has also become hereditarily transmitted, for even 

 those individuals reared in the light lose the color. Numerous 

 facts and experiments show that while pigment may be, and is, 

 developed in total darkness, the amount of color in an individual 

 animal depends, other things equal, directly on the amount of light 

 to which it is habitually exposed. 



The lower and upper surfaces of the flounder, the one protected 

 and the other exposed to the light, give the most striking example, 

 and the argument is clinched here by the fact, noted by Cunning- 

 ham, that a flounder whose lower side is for long periods exposed 



