THE PARS BUCCALIS OF THE HYPOPHYSIS 83 



Early in this section of the paper we stated that two lines 

 of evidence indicated that the neural lobe is dependent upon 

 its epithelial companion for its complete development. These 

 briefly are: 1) certain cellular elements from the pars epithelialis 

 (pars intermedia) apparently migrate into the neural component 

 of the hypophysis and contribute to its secretion; 2) by appro- 

 priate chemical treatment a substance can be secured from the 

 anterior lobe which displays certain of the physiological char- 

 acteristics typical of extracts of the posterior lobe of the pituitary. 

 From this study a third line of evidence from the experimental 

 and developmental work herein detailed has been secured; 3) 

 the neural lobe and pituitary floor are dependent upon the 

 association with the epithelial hypophysis for their full develop- 

 ment. The epithelial hypophysis then appears to exert a stimu- 

 lating effect upon these structures and even upon any adjacent 

 neural tissue, as is shown by the hypertrophy of the neural 

 tissue about the atypically placed epithelial lobe. 



The thyroid 



Sections of the larger albinous larvae show that the thyroid 

 glands of these specimens have suffered a profound atrophy, 

 an atrophy so intense that the remaining vestige could hardly 

 be suspected of playing any important physiological role. That, 

 in fact, this is the case has recently been shown by Allen, whose 

 experimental animals, suffering a double extirpation of the 

 thyroid and buccal portion of the hypophysis, do not differ from 

 those deprived only of the epithelial hypophysis. Indeed, the 

 interrelationship obtaining between the hypophysis and thyroid 

 appears to be of such an intimate nature that the ablation of 

 the former, even in the midlarval stages, effects an atrophy of 

 the latter (Adler, '14). 



The thyroid gland, then, is greatly diminished in size (table 7, 

 figs. 31 to 34) and modified in structure in those tadpoles suffer- 

 ing from an early and complete loss of the epithelial hypophysis. 

 By this atrophy the thyroid is diminished, in tadpoles in excess 

 of 36 mm. total length, to one-sixth or less of its normal size. 



