THE PARS BXJCCALIS OF THE HYPOPHYSIS 29 



Not only are the melanophores darker in the albinos receiving 

 posterior lobe, but the number of these cells is also increased 

 (table 1). Instead of averaging but thirty-eight to the unit 

 area, they average in excess of fifty to this unit area (0.36 of a 

 sq.mm.). Thus both in number and pigment content the epi- 

 dermal melanophores of these animals are intermediate between 

 those of the normal specimens and the typical albinos. "'^ 



It is not on the structural side alone that we find changes 

 with a posterior lobe diet. The epidermal melanophores of 

 these posterior-lobe-fed specimens uniformly exhibit a great and 

 persistent contraction; they are uniformly either rounded or, 

 at most, slightly irregular in shape, appearing as intense dark 

 dots in all areas of the dorsal epidermis (fig. 21). Moreover, 

 this contraction is persistent. After days of the substitution of 

 another diet, it still persists; indeed, under the most potent 

 stimulus — light and heat — for causing an expansion of the 

 epidermal melanophores of the albino, a considerable interval 

 must intervene in which neural lobe is not fed in order to obtain 

 a decisive expansion of these cells. 



It is cxu-ious that no increment in the epidermal melanin was 

 produced in the unoperated tadpoles with a diet of fresh posterior 

 lobe. Not only did no pigmentary increment result, but the 

 contraction of the epidermal melanophores so typical of albinos 

 on this diet did not regularly occur, or at most was but transitory. 



Of the other substances which have been fed, none have ap- 

 preciably affected the epidermal melanophores. One, namely, 

 hver, has produced unmistakable differences, however, in the 

 appearance of the xantholeucophores as contrasted to the albinos 

 upon other diets. This effect is not expressed in any alteration 

 in the usual extreme expansion of these cells, but rather in their 

 color. These specimens do not show the golden sheen of the 

 anterior or posterior lobe or adrenal cortex fed animals, but 

 exhibit a chalky whiteness especially noticeable in the gill regions 

 (figs. 46, 48), an appearance probably due to a reduction in the 

 lipochrome content of the cells. 



" The author has not supplied albinous larvae with posterior-lobe extracts. It 

 is apparent from Allen's work, however, that if they are potent in causing a melanin 

 increase, they must be fed for a considerable interval of time. 



