THE PARS BUCCALIS OF THE HYPOPHYSIS 79 



A study of the older albinous and partially hypophysectomized 

 larvae does not throw light upon the developmental process 

 which has led to the thinning of the pituitary floor and the 

 diminution in the size of the neural lobe in these specimens. 

 From such a study we can conceive that one of two develop- 

 mental processes lead to this anatomical condition. In the first 

 place, it is possible that a normal differentiation and develop- 

 ment of these parts may have taken place, so that at some not 

 very early period they were structurally identical in both the 

 albinous and normal larvae. Later, due to the absence of the 

 association with the epithelial hypophysis, these normally de- 

 veloped parts underwent an atrophy which led to the conditions 

 just described. Or, in the second place, it is possible that, due 

 to the absence of the 'stimulatory' force normally supplied by 

 the epithelial hypophysis, the neural lobe and pituitary floor 

 even from their earliest stages did not undergo the normal 

 increase in size. A developmental study of the albino, the 

 normal, and the partially hypophysectomized tadpole affords 

 clear evidence that the second hypothesis is correct. An exam- 

 ination of the divisions (lateral, saccular, and pituitary) of the 

 infundibular process in an early stage (5 to 10 mm.) reveals the 

 fact that these parts are nearly identical in structure and that 

 no differences exist between a normal larva and a larva which 

 has suffered the loss of its epithelial hypophysis. This infundi- 

 bular pocket, slightly thinner at its apex where it is formed of 

 a cuboidal epithelium, thickens near its attachment to the firmer 

 walls of the brain where it is formed of columnar epithelium. 

 As development proceeds, the dorsal and lateral walls of this 

 pouch become progressively thinner in both the albino and 

 normal animal, and at a 14- to 16-mm. stage their epithelium 

 is of the squamous type and remains so through their larval 

 life span (fig. 10). Thus the development of the dorsal and 

 lateral walls (save the small portion giving rise to the neural 

 lobe) is identical in the two types of animals. It is in the devel- 

 opment of the pituitary wall, however, that the differences 

 between the albinous and normal larvae make their appearance. 

 This portion, both in the albino and the normal, undergoes for 



