20 PIGMENTARY GROWTH AFTER ABLATION OF 



Both layers of corial xantholeucophores are broadly expanded 

 in the albino (figs. 14, 16, 18, 20 to 23, 55 to 58), an expansion 

 which is singularly unamenable, more especially in the older 

 albinos, to altered environmental conditions. To the broad 

 expanse of the refractive cells the albino owes its metallic tone, as 

 can be clearly shown by all procedures which contract these cells. 



We have thus far confined our attention to two types of tad- 

 poles, that type in which the tadpoles have suffered the entire 

 loss of the buccal component of the pituitary, the albino, and 

 that type whose members have suffered no operative inter- 

 ference, the normal. It is now desirable to consider a third 

 type — those in which the epithelial hypophysis was incompletely 

 ablated, the 'partial' albino (figs. 52 to 54). This type of tad- 

 pole usually suffers a serious pigmentary disturbance, its pig- 

 mentary system simulating that of the albino more than that 

 of the normal. In fact, its almost typical albinism frequently 

 makes this animal difficult and often impossible to distinguish 

 during early development from its completely hypophysectom- 

 ized brothers. Later in life it is readily distinguishable, since 

 legs develop in the partially but not in the completely hypophy- 

 sectomized tadpole. In the albinous type of partially hypo- 

 physectomized tadpole as in the typical albino the free pigment 

 is greatly diminished in amount and the epidermal melanophores 

 are scanty in number. That the epidermal melanophores are 

 slightly greater in number than in the complete albino, however, 

 is apparent from counts. It will be recalled that thirty-one 

 counts from five albinos gave an average of thirty-eight epi- 

 dermal melanophores to a unit area 0.36 of a sq.mm. Seventeen 

 similar counts from three 'partial' albinos gave an average of 

 fifty to this unit area (table 1). The xantholeucophores appear 

 to be no way different from those of the typical albino. They 

 exhibit a broad and persistent expansion. Although the pig- 

 ment system of this animal closely resembles that of the albino, 

 yet, in contrast to the albino, it does not suffer serious structural 

 defects in any of its endocrine organs save one, the neural com- 

 ponent of the pituitary. Exhibiting, then, characteristics of 

 both the albino and the normal, this 'hybrid' tadpole has been 



