GEOWTH OF AMPHIBIA AFTER THYROIDECTOMY 11 



Normal Rana sylvatica larvae kept in aquaria and well fed 

 metamorphose normally, but with our thyroidless frog larvae the 

 second season was passed without their metamorphosing. 



Concerning the growth of the thyroidless larvae, it may be 

 noted from tables 1 and 2 and figures 10 to 19 that they ulti- 

 mately became much larger than the control larvae. As stated 

 above, the thyroidless animals grow more rapidly than the con- 

 trols, but the difference is not very great until near the time of 

 metamorphosis. When the controls at this period have nearly 

 reached their maximum length, their growth seems to slacken,, 

 and their length does not change for a short period of time before 

 it starts to decrease during metamorphosis. It is during this 

 time, as was noted also by Allen ('18), that the experimental 

 animals gain very much in size over the controls. In some of 

 our 1918 series measurements of volume of the animals were 

 made at this time and in some cases (table 2) the thyroidless 

 larvae were more than twice as large in volume as the control 

 animals of the same age. The volume was determined by the 

 amount of liquid displaced by an animal. After the metamor- 

 phosis of the controls (1917) the growth rate of the experimental 

 larvae decreased greatly and growth nearly ceased during the 

 winter, but the larvae grew more rapidly during the second 

 spring and summer. For example, the animal shown in figure 

 19 became 55 mm. in length by the time the controls had meta- 

 morphosed in early August, 1917. It was 62 mm. in length on 

 September 2 and 66 mm, on September 27 when next measured. 

 On October 19 the length had not increased. The animal began 

 growing again in May, 1918, but it increased its length by only 

 5 mm. by June 25, and on July 5 had reached its maximum length 

 of 72 mm. with a volume of 2.38 cc, or nearly three times that 

 of the normal larva at the time of metamorphosis. In this 

 growth after the first summer the body length (nose-anus) in- 

 creased 2 mm. and the tail 8 mm. the animal thereby becoming 

 relatively long-tailed. Its hind legs increased after the first 

 season about one-half of a millimeter in length, reaching 5 mm. 

 In these miniature legs the normal segments and digits are 

 slightly differentiated. 



