105 



leucophores appear at the same time and in approximately the 

 same numbers as in the normal, but exhibit from their earliest 

 appearance a broad expansion as compared to the punctate 

 character of these cells in the unoperated tadpole. 



6. The broad expansion of the xantholeucophores and con- 

 traction of the epidermal melanophores of the albino is not due 

 to an alteration in their nervous mechanism, but to the modified 

 tissue fluids which bathe them. This is proved by the reciprocal 

 skin exchanges. That this alteration in the tissue fluids is of 

 a hormonal nature appears probable not only from the known 

 potency of these substances, but also because of the extensive 

 modifications suffered by the elaborators of these substances in 

 the albino. There appears to be no ground for referring the 

 deficiency in the epidermal melanin to other than an internal 

 secretory origin. 



7. Various physiological and pharmacological experiments on 

 the pigmentary system of older albinous and normal larvae 

 reveal the fact that, 1) the deep melanophores of the albino and 

 the normal tadpole react identically under all tests tried by the 

 author; 2) the xantholeucophores of the normal animal respond 

 to changes in environmental conditions, those of the albino, on 

 the other hand, maintain a refractory expansion under all sub- 

 lethal stimuli tried by the author, save that afforded by the pars 

 intermedia emulsion; 3) the epidermal melanophores of the 

 albino invariably expand when subjected to the condition of 

 'light and heat.' Those of the normal tadpole react in a more 

 variable manner, not infrequently exhibiting the opposite reac- 

 tion, contracting instead of expanding. 



8. The thyroid and the adrenal cortex are strikingly dimin- 

 ished in size in the albino; the epithelial bodies suffer a lesser 

 though definite diminution; the adrenal medulla suffers no un- 

 questionable quantitative changes, but it appears not improbable 

 that it is slightly hypertrophied. Structurally, the adrenal 

 medulla is clearly altered in the albino, since its cells are all of 

 a uniformly staining large type, as compared to the variability 

 in size and the diversity in appearance exhibited by the adrenal 

 chromaffin cells of the normal. 



