GROWTH OF AMPHIBIA AFTER THYROIDECTOMY 15 



creases the difference between the relative volume of larvae and 

 frogs. The shortening of the tail and anal canal during meta- 

 morphosis prevents comparison of the larvae and frogs on a 

 basis of the body length (figs. 12 and 16). Given a frog and 

 larva of the same body length (i.e., nose-anus) the latter is two 

 to three times the volume or weight of the former (table 2). 

 If the body length be considered as the distance between the 

 tip of the head and the posterior limit of the body cavity, a 

 larva is more than three times the size of a frog of the same body 

 length. 



In table 2 the measurements of living larvae are given only 

 in the case of the thyroidless animals, as the variation in the 

 controls is similar. The increase in the volume of the control 

 larvae and frogs on account of growth of the legs is offset by a 

 slight increase in the relative length of the tail in the thyroidless 

 animals. 



Regeneration. On April 13, 1918, 12 mm. of the tail and the 

 entire hind legs were removed from a large thyroidless larva 

 from the 1917 series. After fourteen days the tail had increased 

 in length 11 mm. and the body 2 mm. One hind leg had not 

 grown at all, but the other had grown 2 mm. and regenerated a 

 foot that was about half the size of the one removed. The 

 part of the tail that regenerated contained less muscle than 

 normal but was otherwise like the part removed. On April 

 27 an additional 13 mm. of the tail and the regenerated leg and 

 foot were removed. The tail increased again 14 mm. in length 

 in twenty-eight days. The leg did not again regenerate. The 

 body again increased 2 mm. in length. On June 24 an additional 

 12 mm. of the tail was removed and it regenerated 7.5 mm. in 

 twenty-three days. During this period a twist developed in the 

 tail near the body. On July 17 an additional 7.5 mm. of the 

 tail was removed. In five days, 2 mm. of the tail had regen- 

 erated when the animal died. During the three months of this 

 experiment none of the other thyroidless larvae had increased 

 more than 6 mm. in total length, 2 mm. of which growth was 

 in body length, while the experimental animal had regenerated 

 34.5 mm. of tail and its body grew 4 mm. Had it not died, the 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 29, NO. 1 , 



