34 PIGMENTARY GROWTH AFTER ABLATION OF 



definitely expanded (fig. 22) when subjected to heat and direct 

 sunlight. This response becomes more and more marked, until 

 after five weeks we have an almost typical response (fig. 23). 

 The xantholeucophores in these animals as in the typical albino 

 remain broadly expanded under all environmental conditions. 

 Posterior lobe feeding, then, which gives us an epidermal melano- 

 phore system which approaches the normal in melanin content, 

 does not permit these cells to exhibit normal responses to light 

 and heat. It merely maintains them in a refractory and con- 

 tracted state, and when the feeding is stopped they exhibit the 

 typical physiology of the albino. 



The stimuli to which the two types of larvae have thus far 

 been subjected are such as they might meet in the extremes of 

 their normal environment. There is yet another class of stimuli 

 which may be employed, namely, pharmacological agents, in 

 which the larvae may be directly immersed. By this means we 

 may be able to secure further evidence in regard to the endocrine 

 locus responsible for the peculiar functional state of the chroma- 

 tophore groups in the albino. Of the substances employed 

 (pars intermedia emulsion, pituitrin, adrenalin, pineal gland 

 emulsion), the first — pars intermedia emulsion 18 — from the pro- 

 found pigmentary changes which it induces in the albino, es- 

 pecially merits attention. Atwell has called attention to the 

 darkening of albinous larvae when placed in emulsions or ex- 

 tracts of this substance and has noted the response — one of 

 expansion — of the deep melanophores to this treatment, a re- 

 sponse which led him to refer the usual picture of albinism to 

 a contraction of this melanophore group, and conversely the 

 darkening of these treated albinous larvae to the expansion of 

 these cells. We can fully confirm Atwell's observations as 

 pertains both to the darkening of these larvae and the complete 

 expansion of the corial melanophores when placed in the pars 



18 The pars intermedia substance was secured by carefully clipping off pieces of 

 this glandular substance from the subjacent neural lobe, as described by Herring 

 ('14) and Atwdl (IS). Alter drying on a warm plate the powdered substance was 

 triturated with the desired amount of tap-water. 



