REMOVAL OF THYMUS GLANDS TADPOLES . l9l 



Adler ('14) gives the results of a series of experiments upon 

 the larvae of Rana temporaria. The removal of the thymus 

 glands was performed when the half-grown tadpoles had reached 

 a length of 22.5 mm. to 23 mm. This was accomplished by 

 means of an electric cautery. The operation caused a very high 

 mortality. Twenty of the nine hundred tadpoles operated 

 reached metamorphosis, but there was complete absence of the 

 thymus glands in only three individuals and partial absence in 

 five others. We thus find that his results are based upon a study 

 of but three specimens. In the first place, he showed that the 

 removal of the thjanus glands in half-grown tadpoles does not 

 prevent metamorphosis, nor is it accompanied by any external 

 peculiarities. The gonads of these three specimens proved, liow- 

 ever, to be decidedly larger than normal. In only one out of 

 the three were they exceeded in length by any of the specimens 

 in which the operation was unsuccessfully attempted. One un- 

 fortunate feature in Adler' s account is the fact that he gives no 

 statement regarding the sex of the specimens either thymusless 

 or controls. It will be seen in my tables below that the ovaries 

 of young frogs are normally niuch larger than the testes, at least 

 in Rana pipiens. It is quite possible that his three thymusless 

 specimens were all females. The fact that all of the controls had 

 smaller germ glands than did two out of his three thymusless 

 specimens could hardly be accepted as convincing evidence that 

 the removal of the thymus glands has a marked influence in the 

 development of gonads. This objection has especial force when 

 we take into account the fact that Adler only measured the length 

 of the germ glands and did not consider the other dimensions. 



Adler finds that the thyroid glands in these three thymusless 

 frogs are much larger than normal and that they are modified in 

 texture. These points will be discussed below. 



