GROWTH OF AMPHIBIA AFTER THYROIDECTOMY 39 



Ovaries. The left ovary of our animals (R. sylvatica) is nearly 

 always larger than the right ovary. In control and thyroidless 

 larvae of the same size the ovaries are of similar volume within 

 the limits of normal variability (figs. 79 and 80). These thyroid- 

 less larvae are younger than the controls, but of the same size. 

 In larger thyroidless larvae of the same age as the control larvae 

 the ovaries are larger in absolute size than those of the controls, 

 but in relative size they are about the same as the controls, or 

 possibly smaller. 



During metamorphosis the ovaries of the normal larvae (fig. 

 81) change very little in absolute size, beyond perhaps a slight 

 increase; but the decrease of one-half to two-thirds in the size 

 of the body that occurs at this time results in a corresponding 

 increase in the relative size of the ovaries in young frogs, which 

 thus have relatively much larger ovaries than do either the 

 control or thyroidless larvae. 



In the older (and larger) thyroidless larvae the ovaries reach 

 their maximum size at about the same time that the body ceases 

 growing. Figures 83, 84, and 85 show that in July, 1918, the 

 ovaries of some 1917 larvae are very little larger than in the 

 preceding December and October, although the oocytes are 

 larger in the largest animal. The larva in the meantime had 

 also grown slightly. The actual size of the ova will be discussed 

 later. The size of the ovary varies considerably in different 

 larvae of the same size and age, but those shown in the three 

 figures represent the average condition in our 1917 specimens. 

 The third dimension of the ovaries is not well shown in the 

 drawings, but it was studied by the method described above. 



In our 1918 animals which grew very rapidly the ovaries at 

 the normal time of metamorphosis had not grown quite as large 

 as in the 1917 series which grew more slowly (compare figs. 81 

 and 86), but the difference between them is not great. Figure 

 80 shows an ovary of a large but very young 1918 thyroidless 

 larva which still retains the flattened larval shape, although the 

 animal itself was as large as some of the 1917 larvae which were 

 much older and in which the ovaries were further advanced in 

 their development. Hence it is apparent that the time element 



