THE PARS BUCCALIS OF THE HYPOPHYSIS 31 



If we now subject these large animals to the opposite environ- 

 mental conditions (direct sunlight, a white background, and a 

 high temperature 33 to 35), we see a striking change take 

 place. The epidermal melanophores of the normal frequently 

 gradually contract and may ultimately after an hour or even 

 less at times assume only a slightly expanded condition (fig. 19). 

 These cells in the albino, on the contrary, invariably expand, 

 ultimately exhibiting a fully expanded condition (fig. 20). There 

 is thus frequently exhibited a reversal in the reaction of these 

 cells in the large specimens of these two types of animals, 17 a 

 reversal not evinced to its fullest extent with any stimulus tried 

 by the author save that of heat combined with direct sunlight. 

 Either extreme heat or light evokes this reaction to some extent, 

 the relative importance of each factor, however, being difficult 

 to determine. A normal specimen, if placed in the dark at 

 30 to 35, may exhibit after two to three hours partly contracted 

 superficial melanophores. If the temperature becomes normal, 

 these cells expand; if the temperature is maintained and sun- 

 light used, further contraction not infrequently takes place. 

 An albino, if placed in the dark at 30 to 35, exhibits in two 



17 One of the most striking features of the experimental work upon the epidermal 

 pigment cells of the albinous and normal larvae has been the invariable response 

 of these cells in the former as contrasted to their uncertain response in the latter. 

 Of the very considerable number of albinous larvae which have been subjected to 

 the stimulus of 'light and heat' a response, one of expansion, has invariably been 

 exhibited by the epidermal melanophores. In contrast to this stands the variable 

 response of these cells in the normal larvae. Because of the influence which the 

 internal secretory glands have upoq these pigment cells, this invariable response 

 in the albino would appear to be of considerable significance, since certain of the 

 endocrine glands in this type are structurally and also presumably functionally 

 deficient. Consequently, we could expect that the response of these cells in this 

 form would be more certain than in the normal where these cells are under the 

 variable influence of the internal secretory products. 



In 1919 (Proc. Soc. Exp. Biol. and Med., 44-1419) I called attention to the op- 

 posed reaction of the epidermal melanophores in the albinous and normal larvae. 

 The experimental work upon which this description was based was carried out 

 upon the older albinous and normal larvae and should have been so stated. These 

 normal larvae very uniformly exhibited a contraction of their epidermal melano- 

 phores when subjected to 'heat and light' as contrasted to the expansion of these 

 cells in the albino under identical conditions. Subsequent work has revealed a 

 more variable response of these cells in the normal, but not in the albino. 



