68 PIGMENTARY GROWTH AFTER ABLATION OF 



This is well shown by the members of one group (fourteen speci- 

 mens) whose growth rate was more rapid than that of their 

 normal fellows supplied with anterior lobe substance (fig. 9). 

 Moreover, they attained a size notably in excess of that reached 

 by their hypophysis-fed albinous mates. 



Evidently, then, in the case of the frog larvae the enlarged 

 hypophysis, which Allen and Hoskins have shown to result from 

 thyroidectomy, has not supplied any growth stimulus in excess 

 of the normal. To what the acceleration in the toad larvae is 

 due has as yet been undetermined, but that an increased secre- 

 tion from the hypertrophied pituitary may be an important 

 factor, as suggested by Hoskins, seems not improbable. 



4. MODIFICATIONS IN THE SIZE AND STRUCTURE OF THE 



ENDOCRINE ORGANS 



It seems probable that a tissue, whether its distribution be 

 diffuse or localized, is more labile and 'adaptive' in its early 

 formative stage than in its mature condition. An example of 

 this is seen in the nervous system, which in its mature, highly 

 differentiated condition loses its capacity for regeneration and 

 'adaptation,' a capacity which it exhibits to a surprising degree, 

 however, in its early formative stages (Lewis), more especially 

 when associated tissues can elicit a developmental response 

 (Burr). It is likely, then, that if a disturbance be experienced 

 by the endocrine system in its early and embryonic stages, greater 

 alterations in its members will result than if this upset had been 

 suffered later in the life of the individual. As has been pre- 

 viously suggested, the more extensive structural changes which 

 are manifested by the internal secretory organs of the hypophysis- 

 free tadpole as compared to the hypophysectomized mammal arc 

 probably referable to the earlier institution of this disturbance. 

 Extensive structural modifications, as we will show, are invari- 

 ably manifested in the thyroid, the neural portion of the hy- 

 pophysis, and the interrenal and chromaffin components of the 

 adrenal gland subsequent to the early loss of the epithelial 

 hypophysis, while lesser though distinct changes are shown 

 by the epithelial bodies. The behavior of the fat-organ in 

 hypophysial deficiency is also described in this section. 



