THE PARS BUCCALIS UF THE HYPOPHYSIS 11 



(78), Biedermann ('92), Hooker ('12), Redfield ('16); by elec- 

 trical stimulation, Hermann ('86), Winkler ('10), Spaeth ('16, 

 with fish scales); by pharmacological reagents, Lowe ('17); as 

 well as by producing numerical and physiological modifications 

 in the pigment cells by rearing the larvae in different back- 

 grounds, Babak ('13). 6 It is not surprising that a mechanism 

 exhibiting such a functional lability would be modified by dis- 

 turbances in the endocrine system; indeed, that this pigmentary 

 mechanism is influenced by the internal secretory system has 

 been suggested by Fuchs ('14) and Redfield ('16, '18). It was not 

 known, however, until the reports of the writer and of B. M. 

 Allen appeared in 1916 that the ablation of one of the endocrine 

 glands would in itself profoundly and permanently modify the 

 pigmentary system. It was then shown that the early ablation 7 

 of the pars buccalis of the hypophysis induced pigmentary 

 changes leading to the formation of a 'silvery' tadpole — the 

 albino — the most striking pigmentary alteration as yet effected 

 in the tadpole. In this pigmentary disturbance all components 

 of the chromatophore system have been pictured as playing a 

 significant role by various writers. 



The epidermal melanophores have been shown to be dimin- 

 ished in number (Smith, Allen), in pigment content (Smith), 

 and to display a persistent contraction (Allen), all of which 

 has been substantiated in the recent article by Atwell and by 

 the author. It has further been shown that the free melanin 

 which lies near the outer border of the peripheral layer of epi- 

 dermal cells suffers a pronounced diminution (Smith). 



By this diminution in the melanin content of the epidermis, 

 a modification which lends greater transparency to this epithelial 

 covering, the iridescent quality of the subjacent chromatophore 

 group — the xantholeucophores — which in the albino display a 



6 The literature on the pigment cells is stupendous, only a glimpse of it being 

 given here. A complete bibliography on this subject will be found in the compre- 

 hensive article of Fuchs in Wintersteins' Handb. d. vergl. Physiol., Bd. 3, 1 Halfte, 

 2 Teil. 



7 An early operation appears to be essential for the production of a pigmentary 

 effect, since Adler reports no striking pigmentary disturbance subsequent to hy- 

 pophysectomy in the midlarval stages. 



