ENDOCRINE SYSTEM OF TYPHLOMOLGE RATHBUNI. 315 



DISCUSSION. 



The factor which led to the inhibition of the thyroid develop- 

 ment is unknown. The researches of Leo Adler s and Bennett 

 M. Allen 9 showed that extirpation of the hypophysis in amphib- 

 ians inhibits the development of the thyroid. One could imagine 

 that defective development of the hypophysis might have been 

 the immediate cause of the inhibition of the thyroid development 

 in Typhlomolge, but so far, no abnormalities in the structure or 

 mutual relations of the various parts of the hypophysis have been 

 discovered, which could account for the thyroid atrophy of 

 Typhlomolge a phenomenon singular in the vertebrates. 



It is not known whether the atrophy of the thyroid of Typhlo- 

 molge is only one of the results caused by certain factors which 

 lead to the inhibition of the general development of this animal, 

 or whether the inhibition of the thyroid was primary to other 

 developmental inhibitions. As pointed out in previous papers 10 

 the athyroidism of this species possesses special interest, because 

 in the same species metamorphosis also is suppressed. I have 

 assumed, in a purely tentative manner and in order to obtain a 

 basis for further experiments, that the latter phenomenon is the 

 direct result of the lack of the thyroid. In the absence of ade- 

 quate experiments and in the light of the well known fact that 

 extirpation of the thyroid inhibits the amphibian metamorpho- 

 sis u , 12 , this explanation still seems to be the most feasible one. 



Swingle, 13 in a recently published article, takes occasion to 

 criticise my attitude, outlined above, towards the problem of 

 neoteny in Typhlomolge. He has made certain observations con- 

 firming the existence of a releasing mechanism in salamanders. 

 Regarding the facts communicated in this article, these surely 

 should be welcome to the writer of the present article, in so far 

 as they led Swingle to exactly the same conclusion as that at 

 which I arrived as early as 1919. But certain statements 

 made in this paper are apt to give rise to misunderstandings. 

 To prevent these a discussion of Swingle's paper seems desirable. 



8 Adler, L., Arch. Entwcklgsmech. d. Org., 1914. XXXIX., 21. 



9 Allen, B. M., Biol. Bull., 1917, XXXII., 117. 



10 Uhlenhuth, E., Endocrinology, 1922, VI., 102. 



11 Allen, B. M., Science, 1916, N. S. XLIV., 755. 



12 Hoskins, E. R., and Hoskins, M. M., Jour. Exp. Zoo/., 1919, XXIX., i. 

 "Swingle, W. W., Jour. Exp. Zoo/., 1922, XXXVI., 397. 



