EEMOVAL OF THYMUS GLANDS — TADPOLES 



193 



Four of these thymusless specimens were oedematous at the time 

 of metamorphosis. Three died while the tail was fairly long, i.e., 

 between 15 and 20 mm. in length. In all cases, however, the 

 fore limbs were well developed and in none was the tail longer 

 than the trunk. During the ensuing season the experiment was 

 repeated, adding four cases of complete thymus removal and 

 two cases in which it was incomplete. In none of these was there 

 oedema nor was there marked mortality during metamorphosis 



Proneph 3-5 G.P. 



r*G.p. 



as in the season before. This is good evidence that these alD- 

 normalities were not due to the absence of the thymus glands. 

 In fact, the evidence in favor of such an interpretation was slight 

 enough on the basis of the 1917 experiments, one of the controls 

 having shown the same degree of oedema. 



The specimens were fixed in bichromate acetic. The utmost 

 care was taken to search for the thymus glands or any possible 

 remnants of them in the oj^erated tadpoles. In five cases the 

 entire head was sectioned as far back as the region of the fore 

 limbs. The material having been previously stained in toto 



