324 EDUARD UHLENHUTH. 



any theories, aside from those directly suggested by the results 

 of my experiments, as to the nature of the releasing mechanism ; 

 devoting pages to discussing assumptions and hypotheses does 

 not materially advance the problem. We know, of course, that 

 the hypophysis has something to do with the development and, 

 possibly, with the function of the thyroid. I have made some 

 experiments, to be published shortly, which seem to indicate that 

 some unknown factor is located in the gills, in the absence of which 

 the thryoid, although it develops in a normal manner, remains 

 incapable of releasing the hormone. Swingle mentions one ex- 

 periment which was intended to test the activity of the hypophy- 

 sis of a neotenous axolotl by the grafting method. Although 

 ultimately it may turn out that the hypophysis controls, in some 

 way, the releasing mechanism, Swingle has so far contributed 

 nothing to the solution of this problem. 



Hence it is very evident that Swingle has not advanced, by a 

 single step, the problem of neoteny and thyroid function beyond 

 the stage at which my own researches left it. 



SUMMARY. 



1. Only in one, a sex-mature specimen, among 7 specimens of 

 TypJiIomolge rathbuni, is the thyroid completely absent; in the 

 other 6 specimens rudiments of the thyroids are present. 



2. The thyroid rudiments are undifferentiated epithelial cell 

 masses located along the path of migration of the thyroid, typical 

 for salamanders. They may contain a lumen, but never contain 

 colloid and blood vessels. 



3. Typhlomolge possesses 3 pairs of thymus glands. 



4. The hypophysis is similar to that of other salamanders. 

 But the partes tuberales are perhaps smaller than in the adult 

 A . opacum and the pars nervosa is larger. 



5. The postbranchial body resembles much that of other sala- 

 manders, but sometimes is shorter and lacking a lumen. 



