GEOWTH OF AMPHIBIA AFTER THYROIDECTOMY 43 



Testes. The left testis in our animals is usually larger than 

 the right. In our 1918 series where the size of the testes at 

 various ages was studied we noted that within normal variability 

 the testes of the control larvae before metamorphosis were of 

 the same actual volume as those of thyroidless larvae which 

 were the same size as the control larvae. The testes of the 

 controls were also of the same relative volume as those of larger 

 thyroidless larvae which were of the same age as the controls 

 (figs. 88 and 89). 



The testes were studied from camera-lucida drawings much 

 larger than those shown here and were compared also by the 

 method described above, whereby two organs to be compared 

 are placed side by side under a high-powered binocular dissect- 

 ing microscope and their relative volumes estimated with the 

 eye. One does not try to reduce such volumes to figures, but 

 figures so obtained would not be much more inaccurate than 

 those obtained by multiplying together three principal dimen- 

 sions of an organ, as is sometimes done. Small differences could 

 not be determined by either method. 



The normal variability in the size of the testes is very great. 

 During metamorphosis they do not decrease in absolute size as 

 do many somatic structures, but usually gain very slightly (fig. 

 90). The decrease in the size of the entire animal during meta- 

 morphosis results in a very decided increase (100 to 300 per cent) 

 in the relative size of the testes, so that a young frog has rela- 

 tively much larger testes than either the control larva from 

 which it is transformed or a thyroidless larva of the same size 

 or age of this control. 



In our 1918 animals which grew very rapidly the testes de- 

 veloped actually more rapidly (as did the ovaries) than in the 

 1917 group, but more slowly in relation to the development of 

 the body as a whole. This was shown by the fact that the testes 

 of the 1918 animals were still in the flattened elongated larval 

 shape even after the period of metamorphosis (figs. 89 and 90), 

 whereas those of the 1917 animals had become elipsoid like the 

 testes of frogs and of older thyroidless larvae (figs. 91 and 92). 

 In the thyroidless larvae of 1918 the testes had become rounded 



