8 PIGMENTARY GROWTH AFTER ABLATION OF 



apparently rule out one of the common California frogs, R. 

 aurora dratonyii, as well as the newt. The frog, Rana boylei 

 Baird, and to a limited extent the toad, Bufo boreas, were utilized 

 in this work and have proved very satisfactory, since they re- 

 cover quickly from the operation, are vigorous feeders, and 

 exhibit a rather uniform rate of growth. 



The anlage of the epithelial hypophysis can be more easily 

 ablated than any of the other glands of internal secretion save 

 the thyroid. As is well known, this ectodermal invagination, 

 lying between the brain and the pharynx, is connected with the 

 surface epithelium in very young frog larvae, 3 and is conse- 

 quently readily accessible (fig. 12). If a transverse cut with 

 finely ground needles be made through the surface ectoderm 

 between the forebrain protuberance and the pharynx 4 (figs. 11, 

 12) and these two structures gently separated, the hypophysial 

 ingrowth is readily distinguished lying on the ventral surface 

 of the brain, from which it can be separated without serious 

 injury to the latter. The stage selected for the operation should 

 neither be too young, in which case the structures are undiffer- 

 entiated and serious injury may be done to the mouth, nor too 

 old, in which case the hypophysis will have migrated to its 

 deeper position, thus making its removal extremely difficult. 

 Larvae of 33/6 to 4 mm. in length, at which time the tail bud is 

 well formed and the nasal placodes distinct, appear to be in 

 the most favorable stage for epithelial hypophysectomy (fig. 11). 

 Since reflex movement has not yet appeared, no anaesthetic is 

 necessary. 



It is essential to furnish a continuously renewed supply of 

 well-aerated water to the larvae. In this locality the added 

 necessity of 'sterilizing' the water by heat at 60C. for at least 

 an hour, followed by cooling and reaeration, has been forced 

 upon us (Smith, '18), because of the pathogenic organisms which 



3 Excellent descriptions of the development of this structure in Amphibia have 

 been given by Orr ('89), Corning ('99), Kingsley and Thyng ('04), Atwell ('18), 

 and others. 



4 A depression at the point of invagination of the hypophysis plainly marks its 

 position (figs. 11, 12, Hyp. p.). With later development this pit gradually dis- 

 appears or merges into the stomodaeum. 



