Reaction of Pigment Cells in Frog Larvae. ' 79 



the hypophysis, a pigmentary system is produced which is not 

 only strikingly different from the normal in its anatomical and 

 physiological condition but also exhibits striking departures from 

 the normal in its physiological responses. 



Normal larvae kept in diffuse light and on an indifferent back- 

 ground usually show a fully expanded, or only slightly contracted, 

 condition of the epidermal melanophores 1 and a completely con- 

 tracted, or but slightly expanded, condition of the corial xan- 

 tholeucophores. This condition can almost always be somewhat 

 exaggerated by submitting the larvae to the simultaneous action 

 of low temperature and darkness, when the epidermal pigment 

 cells are fully expanded and the corial xantholeucophores minute, 

 silvery dots. When such larvae, or those from an indifferent 

 environment, are submitted to reverse conditions, i. e., the simul- 

 taneous action of warmth (33°-35° C.) and sunlight, these two 

 classes of pigment cells react in the reverse way and in from one 

 half to one hour exhibit a picture of contracted melanophores 

 and widely expanded silver cells. It is thus seen that the reactions 

 of the two groups of superficial pigment cells — the epidermal 

 melanophores and the corial xantholeucophores — go hand in 

 hand and are in a reverse direction. 



Attention has already been called to the constant great ex- 

 pansion of the corial xantholeucophores in the albinos, an ex- 

 pansion which exceeds considerably that which can ever be ob- 

 tained by the action of sunlight and heat on normal larvae. More- 

 ever, it is difficult to influence by physiological means this great 

 expansion of the xantholeucophores in the albino. On the other 

 hand, the epidermal melanophores of the albinos, which exhibit 

 various stages of contraction, are widely expanded by the action 



1 This condition is the same as that characterizing the deep melanophores which 

 harmonize in their behavior under exaggerated conditions of light and temperature 

 with their more intimate associates, the xantholeucophores. The reactions of the 

 deep melanophores have been the object of considerable study and in the experience 

 of the writer are identical in albinous and normal individuals. Attention must again 

 be called to the necessity in all experiments of this type of not merely submitting 

 the animals and their controls to identical conditions, but also to start with a known 

 physiological condition which has been produced by the action of a practically con- 

 stant environment over a considerable period of time preceding the experiment, the 

 effect of which upon the larvae is known through careful examination of the living and 

 unanaesthetized specimens immediately preceding the tests. 



