THE PARS BUCCALIS OP THE HYPOPHYSIS 21 



of especial value in freeing any of the other endocrine glands 

 which have been studied from responsibility for the pigmentary 

 disturbance, as will be later shown. 



An examination of the pigmentary system of the albino has 

 revealed that one group of chromatophores, the xantholeuco- 

 phores, exhibits a great expansion; another group, the epidermal 

 melanophores, is diminished both in number and pigment con- 

 tent and displays an unusual contraction. It is necessary, then, 

 to examine the developmental stages leading to the production 

 of the characteristic albino if we wish to determine whether 

 this is a progressive phenomenon; whether from the beginning 

 the formation of the epidermal melanophores, for example, is 

 inhibited by the endocrine fault, or whether on the other hand 

 they form only to partially disappear later. The three groups 

 of pigment-bearing cells make their appearance in the following- 

 sequence: deep melanophores, xantholeucophores, epidermal 

 melanophores. A period of several days intervenes between the 

 appearance of each of these groups, and so they may well be 

 treated independently in a developmental study. 



The time of appearance of the deep melanophores apparently 

 is identical in both the normal and hypophysectomized tadpole. 

 In a 6 to 7 mm. stage for the normal, they have already made 

 their appearance in the dorsal regions of the head and body. 

 A few show the typical shape of the deep melanophore. A 

 majority, however, have longer and more delicate processes than 

 the typical corial melanophore. They either lie well separated 

 from the epidermis or, especially where the epithelium closely 

 approximates the underlying firm structures, may be in contact 

 with the epithelial covering. From this "stage they progressively 

 increase in number and gradually become organized until they 

 attain the typical arrangement as a corial sheet at a 10 to 12 mm. 

 stage (fourteen to twenty days after the operative stage). 



The xantholeucophores make their appearance in larvae of 

 10 to 11 mm. (fourteen to sixteen days after the operative stage), 

 appearing concomitantly both in time and number in the normal 

 and hypophysectomized larvae. Slightly more numerous, pos- 



