132 W. W. SWINGLE 



Laurens, working on Amblystoma larvae, states that the epidermal 

 melanophores of this form expand and contract, and hence appear 

 to play an active role in pigmentation changes. The recent 

 work of Smith likewise indicates that this type of pigment cell is 

 contractile. 



In this connection it is interesting to note that following hypo- 

 physectomy the resulting albino larvae appear to lose their epi- 

 dermal melanophores to a large extent, and according to A twell 

 ('19) the few that remain contain only a small proportion of the 

 normal number of pigment granules found in similar cells of the 

 control larvae. Allen ('17) thinks that following removal of the 

 pituitary, the epidermal pigment cells migrate to deeper positions 

 in the animal, a conclusion with which Smith disagrees. However 

 this may be, transplantation of the pars intermedia causes the 

 appearance of large numbers of this type of melanophore in 

 the skin of the bullfrog tadpole, though there can be little doubt 

 that the dark color of the engrafted animals is due chiefly to the 

 subepidermal melanophores. It is highly improbable, as Smith 

 has shown, that the corial chromatophores play an important role 

 in the picture of albinism resulting from hypophysectomy, no 

 matter whether they are contracted or expanded, because they 

 are completely masked by the broad and persistent expansion of 

 the layers of xantholeucophores above them. 



Transplantation of the pars intermedia brings about contrac- 

 tion of the xantholeucophores, thus enhancing the 'darkening' of 

 the larvae. In the present discussion we are not concerned with 

 this type of pigment cell. 



DISCUSSION 



The role of the hypophysis in producing pigmentary changes in 

 anuran larvae has received considerable attention since the pub- 

 lication of the work of Smith ('16) and Allen ('17) on hypo- 

 physectomy in the frog embryo. Both of these investigators, 

 working independently, succeeded in ablating the epithelial 

 anlagen of the hypophysis at the time of its first appearance as a 

 wedge-shaped invagination of cells from the oral ectoderm. 

 Within a few days following the operation the tadpoles lose their 



