THE PARS BUCCALIS OF THE HYPOPHYSIS 37 



is usually a contraction, although sometimes preceded by a 

 preliminary expansion. With the smaller amounts these cells 

 usually expand, there then being presented in the more favorable 

 cases xantholeucophores of approximately the same size, both 

 in the albino and in the normal. 



The deep melanophores of both albinous and normal larvae 

 contracted by a solution of pineal glands (two beef glands in 

 150 cc. water), the same transparency being exhibited as after 

 adrenalin." This contraction of the deep melanophores, which, 

 as pointed out, can be produced by darkness as well, somewhat 

 intensifies the albinous appearance of true albinos, but its ex- 

 treme effect in no case renders normal larvae albinous in appear- 

 ance. These facts are of service in the evaluation of the relative 

 significance of the various groups of pigment cells in producing 

 the picture of albinism. 



The anatomical and physiological findings which have been 

 detailed may now be reexamined in order that we may be able 

 to evaluate the relative importance which the various com- 

 ponents of the pigmentary system have in creating the picture 

 of albinism. Any explanation of structural or functional causes 

 for the albinous appearance must keep clearly in mind the ar- 

 rangement of these pigment cell types. It will be recalled that 

 the deepest group of pigment cells — the corial melanophores — 

 are overlaid by double strata (in most regions of the body) of 

 xantholeucophores, which in turn lie beneath the epidermal 

 pigment formed by the double component of free melanin and 

 epidermal melanophores. With this arrangement in strata it 

 is obvious, then, that a decrease in the color depth of an over- 

 lying stratum will exaggerate the effect of the subjacent one, 

 or conversely an increase in the color depth of a stratum will 

 proportionately decrease the color effect of those lying beneath. 

 The decrease in pigment which obtains in the superficial pig- 

 ment layer (epidermal) of the albino then exaggerates the chro- 

 matic effect of the abnormally expanded subjacent strata of the 



^' With neither of these agents was the extreme transparency gained which Mc- 

 Cord and Allen describe. Indeed, it is difficult to conceive how such an extreme 

 effect could be produced with the very considerable amount of melanin which the 

 epidermis of these specimens contains. 



