PIGMENT CHANGES IN ANURAN LARVAE 137 



embryo frog is accounted for, but not the diminution in number 

 and melanin content of the epidermal melanophores. On the 

 other hand, if, as stated by many workers on pigment cells, the 

 expanded condition is the active phase, then we are faced by a 

 difficult problem when considering the albino, for unless the al- 

 ternative proposition, that some other internal secretory mechan- 

 ism is at work along with the pars intermedia, is adopted, we must 

 assume that an 'absence' can bring about very positive differ- 

 ential results within a single system. 



In conclusion, the writer takes this opportunity to express his 

 obligation to Miss Julia E. Lovett, of the Osborn Zoological 

 Laboratory, for the excellent drawings. 



LITERATURE CITED 



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1920 Experiments in the transplantation of the hypophysis of adult 



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