THE PARS BUCCALIS OP THE HYPOPHYSIS 39 



viously been noted. It thus appears evident that the role of 

 the deep melanophores in the formation of this picture of al- 

 binism is of no great importance. In fact, they are so completely 

 masked in the body region in the albino by the overlying, broadly 

 expanded xantholeucophores that from the anatomical arrange- 

 ment alone it would be apparent that in R. boylei they could 

 play no significant role in the formation of this picture, and most 

 certainly not the primary role as maintained by Atwell in R. 

 sylvatica. 



It is also possible to test the relative significance of the dimin- 

 ished pigment content of the epidermis in the formation of this 

 albinous picture. Attention has been called to the partial 

 replacement of the pigment deficiency which takes place with 

 a posterior lobe diet, and it was seen that these larvae became 

 distinctly darker in color than the albinos not supplied with 

 this gland. Or again, in the skin exchanges, the normal graft, 

 whose xantholeucophores become broadly expanded, neverthe- 

 less is decidedly darker than the albinous host. This color 

 depth can be referred in both cases in part to the color directly 

 contributed by this epidermal melanin and in part to the masking 

 of the underlying xantholeucophores by this pigment. It thus 

 seems clear that the anatomical factors chiefly involved in the 

 picture of albinism are, first, the broad expansion of the xantho- 

 leucophores; second, the diminution in the epidermal melanin 

 which permits full display of the refractive xantholeucophores. 



The greatest interest attaches to the determination of the 

 endocrine locus responsible for the altered structural and physio- 

 logical state of the pigment cells. Attention was called to the 

 fact that the feeding of neither anterior lobe, adrenal cortex, 

 adrenal medulla, nor liver deepened the color of the albino. 

 On the other hand, a diet of posterior lobe (and associated pars 

 intermedia) materially darkened the albino an effect immedi- 

 ately referable to a partial replacement of the epidermal melanin. 

 Also the immersion of the larvae in a solution of pars intermedia 

 alone, of all the endocrine extracts employed, produced a normal 

 physiological condition of the chromatophore system. It would 



