30 PIGMENTARY GROWTH AFTER ABLATION OF 



The responses of the chromatophores to various physiological and 

 pharmacological agents 



It has been shown that the pigment cells of both the normal 

 and the albinous tadpole are influenced by the internal secretory 

 system. Since the endocrine system is abnormal in the albino, 

 it is logical to inquire whether the atypical pigmentary system 

 of these specimens will react to various stimuli as does this sys- 

 tem in the normal animal. 



Although we can largely confirm Laurens' observations (made 

 on Amblystoma) upon the irregular reactions of the epidermal 

 melanophores, it will be recalled that in the unoperated tadpole 

 the usual state of these cells under indifferent environmental 

 conditions — diffuse light and a gray background — is one of 

 two-thirds to full expansion. The xantholeucophores, on the 

 contrary, are punctate or slightly expanded, while the deep 

 melanophores are fully expanded. 



The usual condition of the epidermal melanophores of an 

 albino in our so-called 'indifferent' environment was one of 

 complete, or nearly complete, contraction. The xantholeuco- 

 phores, on the contrary, are broadly expanded. 



If we now place a large albinous and a large normal" specimen 

 in the dark for a period of one to two hours at room temperature, 

 we find certain well-marked changes take place. The epidermal 

 melanophores of the normal, if not completely expanded, become 

 so, but those of the albino being previously greatly contracted 

 are unaffected. The xantholeucophores of the normal become 

 punctate; these cells in the albino remain fully expanded. The 

 deep melanophores of both animals become greatly contracted, 

 the animals then displaying a 'transparency' typical of the con- 

 tracted condition of these cells. A low temperature (0° to 15°) 

 apparently does not increase the reaction to any extent, the 

 epidermal melanophores of the albino surely not being affected. 



" As complete an analysis of the reactions of the epidermal melanophores in the 

 young normal tadpole as could be desired has not been made. The reactions here 

 described unless otherwise stated apply only to large larvae at a time shortly pre- 

 ceding metamorphosis (in the normal). 



