THYROID REMOVAL IN LARVAE OF RANA PIPIENS 517 



In these experiments, artificial neoteny has been definitely 

 produced. Sexual maturity was attained in the male and it is 

 altogether probable that it may be reached in the course of time 

 in the female tadpoles. Just as in the classic case of the axolotl, 

 sexual maturity is reached with a persistence of larval form. It 

 is possible that neoteny of the axolotl is due to the failure of 

 the thyroid gland to attain its full development of structure or 

 function. 



SUMMARY 



1. Absence of the thyroid gland in the tadpoles of Rana pipiens 

 does not affect the course of early development up to the time 

 when the hind limbs have begun to grow. 



2. Further differentiation of the soma then ceases and meta- 

 morphosis does not occur. In the present paper, the following 

 features of soma development have been studied with the result 

 that no continuation of differentiation was observed in the fol- 

 lowing features. 



a. The general body form and limb development. 



b. The alimentary tract in its entirety. 



c. The brain. 



Although special studies of other organs were not made, there 

 was no evidence that any of them, except the gonads, showed 

 further differentiation. 



3. The anterior portion of the head shows an abnormal form, 

 being lengthened and broadened. 



4. Thyroid administration to thyroidless tadpoles brought 

 about a resumption of development even four months after it 

 had ceased. 



5. The removal of the thyroid gland has no effect of any kind 

 upon the gonads and germ cells. This is in significant contrast 

 to the effects upon all the other portions of the body. 



LITERATURE CITED 



Guderxatsch, J. F. 1912 Feeding experiments on tadpoles. Arch. f. Ent- 

 wicklngsmechn. d. Organ., vol. 35, p. 457. 



1914 A further contribution to the knowledge of organs with internal 

 secretion. Am. Jour. Anat., vol. 15, p. 431. 



