18 PIGMENTARY GROWTH AFTER ABLATION OF 



condition obtaining in these cells in the albino is one of com- 

 plete, or nearly complete, contraction. 



The free pigment which forms a definite, though imperfect, 

 layer in the normal animal is much diminished in amount and 

 is irregularly distributed in the albinous larvae (figs. 13, 14). 

 In the skin whole mounts of the albino, it indeed forms but a 

 scanty and irregular sheet which stands in contrast to the very 

 distinct layer present in the normal animal. 



The deep melanophores. The number and melanin content 

 of the deep melanophores apparently are not altered by the 

 ablation of the hypophysis. This structural independence ap- 

 pears not to lend support to those investigators who" assert that 

 both groups of melanophores, epidermal and corial, arise from 

 a common source. 12 



That the deep melanophores exhibit a contracted condition 

 has been noted by Allen and Atwell, the latter, indeed, referring 

 the phenomenon of albinism primarily to their contracted con- 

 dition. Many examinations of larvae in excess of 45 mm. in 

 length, made both on the living animal and after rapid fixation, 

 convince the author beyond question that in the body and head 

 regions these cells, whether occurring in the corium, in muscle 

 sheaths, or in the fascia of the viscera and body cavities, exhibit 

 nearly the same physiological state in the fully developed albino 

 of R. boylei as in the normal (figs. 13, 14) ; in the young albino, 

 however, certain of these cells appear to be in various stages of 

 contraction (fig. 16). 



The xantholeucophores. We have noted significant and con- 

 stant changes in the superficial layer of the first group of pig- 

 ment cells the bearers of melanin. Changes no less significant 

 in the phenomenon of albinism are encountered in the second 

 group of chromatophores, the bearers of guanine and xanthine. 

 Indeed, since the silvery and iridescent characteristics of many 

 fishes are referable to these cells, it would seem to make them of 

 paramount importance in the phenomenon of albinism. When 

 viewed by transmitted light, these cells are of a grayish or brown- 



12 Ehrmann ('96 and earlier) refers the common origin of the melanophores to 

 the mesoblast of the dorsal cephalic region of the body. 



