GROWTH OF AMPHIBIA AFTER THYROIDECTOMY 41 



of the body, as other organs are equally independent in their 

 development. 



Oviducts did not develop in the animals kept through the 

 second season, so sexual maturity cannot be said to have been 

 reached, and the condition is not true neoteny, according to 

 the present definition of that term. 



Microscopic structure. Figures 94 to 103 represent the micro- 

 scopic structure of the ovaries of animals in various stages of 

 development. Synapsis begins often in normal larvae when the 

 animals are but 25 mm. long and only about one-fourth grown. 

 The great variation in the time of synapsis prevents a determi- 

 nation as to whether thyroidectomy stimulates this process di- 

 rectly, although it is clear that an indirect influence is exerted 

 by the rapid growth of the thyroidless larvae. 



The question of the relation between the differentiation of 

 gonads and that of the body is very complex. While the former 

 is not entirely independent of the latter, it is far from being 

 dependent on it, as a study of the accompanying figures (94 to 

 103) shows. In the 1917 animals, which did not receive an 

 optimum food supply and which grew slow^ly, the ovaries at 

 metamorphosis showed well-developed oocytes 120 /^ in diameter 

 (fig. 96). The ovary of a very small precocious frog (fig. 95) 

 was actually smaller than that shown in figure 96, but relatively 

 larger. Oogenesis in it had progressed faster than in the normal 

 animal, but the oocytes were smaller, being not more than 75 m in 

 diameter. The control specimen of the precocious frog was at 

 this time a larva 40 mm. long, with ovaries smaller than that 

 of the frog and with oogenesis less advanced. 



In contrast with the above relations, it was found in 1918 

 that in normal larvae at the time of metamorphosis, in thyroid- 

 less larvae of the same size, and in young frogs, all of which had 

 grown rapidly, the ovaries were but slightly differentiated (fig. 

 97) and were smaller than those of the corresponding animals 

 of 1917. The oocytes in the 1918 specimens were not more 

 than 50 ix in diameter, about the size of those found in some 

 half-grown 1917 larvae. The problem is further complicated by 

 the fact that in the larger 1918 larvae which grew much more 



