METAMORPHOSIS IN FROG LARVAE 523 



Biedl extirpated the thyroids of dogs, three to five weeks of 

 age, and among other changes observed was a noticeable hypo- 

 plasia of the sexual glands. This investigator claims that the 

 arrest in development of the sexual organs is one of the typical 

 and invariable results of the absence of the thyroid function in 

 both carnivora and herbivora. 



The clinical evidence, derived from cases of athyrosis in man, 

 that the thyroid appears to be related in some way to the sex 

 glands physiologically, is rather striking at first glance. For 

 illustration: One of the most constant symptoms of thyroid 

 insufficiency in young, growing individuals is the infantilism 

 of the sexual organs, in consequence of which puberty is very 

 much retarded or else absent altogether. Furthermore, in myx- 

 oedema, a disease due to suppression of the thyroid function, there 

 is frequently disturbance of the sexual functions. Also, in certain 

 other diseases, such as infantilismus myxoedematosus and cretin- 

 ism, there is usually imperfect development of the sexual organs. 



So far as the present writer is aware, the experiments and 

 clinical evidence just presented, represent the extent of present 

 day knowledge concerning the relation of the thyroid to the 

 sex glands. In none of the work quoted here is there any con- 

 clusive evidence regarding the direct action of the thyroid secre- 

 tion upon the gonads; all that is shown is that full sexual de- 

 velopment apparently depends upon the presence of the thyroid 

 gland. In view of the physiological relation known to exist 

 between the thyroid and other glands of internal secretion and 

 in turn between the latter and the gonads, it is very probable 

 that the action of the thyroid is indirect and exerts its influence 

 through the intermediation of other glands. 



Concerning the effect of thyroid feeding upon frog larvae, 

 there is a growing list of experiments upon these animals since 

 Gudernatsch first published his results. This author fed the 

 larvae of Rana temporaria upon thyroid gland and found that 

 the growth of the tadpoles soon ceased, and the tail began to 

 atrophy and metamorphosis began. He was able to produce 

 pigmy frogs, no larger than flies, by thyroid feeding. No report 

 was made as to the condition of the gonads. 



