PIGMENT CHANGES IN ANURAN LARVAE 133 



normal dark coloration and turn silvery white, or, according to 

 Smith, they become albinos. The pigmentary change is char- 

 acteristic and striking. 



Smith and Allen hold somewhat different views regarding the 

 nature of the change in pigmentation following hypophysectomy. 

 Smith considers the silvery appearance of the larvae as being 

 due primarily to a reduction in number and melanin content of 

 the epidermal melanophores, and to persistent expansion of the 

 xantholeucophores. The expansion of the latter gives the tadpole 

 its silvery appearance. He states that the corial melanophores 

 are equally expanded in the albinos and the control animals. 



Allen, on the other hand, believes that the albino effect is due 

 to the migration of the epidermal pigment cells to deeper positions 

 in the body and, moreover, that all the melanophores throughout 

 the body are contracted following ablation of the epithelial 

 portion of the pituitary. 



Neither of these investigators had any good evidence as to just 

 what portion of the hypophysis is responsible for the change in 

 color following extirpation, for in their experiments three parts of 

 the hypophysis were removed, anterior lobe proper, pars inter- 

 media, and the pars tuberalis. It remained for Atwell ('19) to 

 show that it is the lack of the pars intermedia that is responsible 

 for the albino appearance of the hypophysectomized larvae. He 

 extirpated the hypophysis of the frog embryo and, following the 

 'silvering' of the tadpoles, placed them in dilute extract of pars 

 intermedia of beef pituitary. The animals soon underwent a 

 striking color change from silvery to dark, in the latter condition 

 closely resembling normal tadpoles. When returned to fresh 

 water the darkened larvae regained the silvery appearance. 



Atwell interpreted his results as indicating that the ' silvering' 

 of the hypophysectomized larvae was due to a prolonged and sus- 

 tained contraction of the pigment-bearing cells, owing to loss of 

 the pars intermedia. Smith, in his recent monograph, puts a 

 different interpretation on Atwell 's work He confirms Atwell's 

 observations that the corial melanophores expand in solutions of 

 pars intermedia, but he noted further that not onl^^ do the larvae 

 become darker, but they almost completely lose their metallic 



THE JOURNAL Or EXPERIMENTAL ZOOLOGY, VOL. 34, NO. 2 



