THYROID REMOVAL IN LARVAE OF RANA PIPIENS 515 



Since the female of February 14 is a crucial stage, a series of 



ten slides through the thyroid region was made and carefully 



searched for remnants of thyroid tissue. None were found. 



This demonstrates that this specimen is truly devoid of a thyroid 



gland. 



CONCLUSIONS 



This work gives results which are in complete harmony with 

 those attained by Gudernatsch, Swingle and others in their ex- 

 periments in feeding thyroid gland preparations. While Guder- 

 natsch showed that thyroid feeding accelerates development, this 

 work shows that the total absence of the thyroid gland produces 

 complete cessation of somatic differentiation at a certain stage 

 but does not hinder continued growth in size. It is especially 

 interesting in this connection to find that the early organogenesis 

 continues unhindered, up to a certain point. This applies even 

 to the early development of the hind limbs and of the fore limb 

 rudiments. The former undergo the beginnings of ossification, 

 as shown by Terry, while the fore limb rudiments never show the 

 slightest sign of breaking through the skin. 



It is evident that the thyroid gland is in no wise essential to 

 the earlier phases of developent, but that at a certain definite 

 stage, further development of the soma is dependent upon it. It 

 is impossible to attribute this early normal development to the 

 persistence of secretions given off prior to the operation, be- 

 cause the thyroid anlage is removed at its very inception and 

 the effects do not become evident for from two and a half to 

 three months. 



The most remarkable result of this investigation is the demon- 

 stration of the sharp difference between its effects upon the 

 gonads and upon the remainder of the body. This had been 

 demonstrated from a different angle by Swingle who, working 

 under my direction, fed thyroid preparations to tadpoles and 

 studied the effects upon the gonads and germ cells. Much to 

 our surprise, they went their normal course unaffected by the 

 great acceleration of body growth. A report on this work was 

 made at the Columbus meeting of the A. A. A. S. in 1915 and 

 Swingle gives a full account of his work in the current issue of this 



