ENDOCRINE SYSTEM OF TYPHLOMOLGE RATHBUNI. 321 



spontaneously. Early in his work he began to select carefully 

 individuals which produced 100 per cent, neotenous larvae. 



Swingle also quotes the experiments of Huxley and Hogben, 24 

 and of Hirschler 25 against me. What Huxley and Hogben really 

 found, however, is that inorganic iodine does not enforce the 

 metamorphosis of axolotls. There are still Hirschler's experi- 

 ments; these are represented by "one" successful experiment. 

 The total number of Hirschler's experiments on inorganic iodine 

 in relation to axolotl metamorphosis is "two." One animal was 

 given an intraperitoneal injection of iodoform; it died before a 

 conclusive result was obtained. The other animal received an 

 injection of iodine dissolved in potassium iodid; it metamor- 

 phosed completely. But the animal illustrated, as a control 

 alongside this experimental animal, shows, contrary to the authors 

 claim, distinct signs of metamorphosis, a reduction of the tail 

 fin and instead of the larval gills mere stubs. It seems to me the 

 number of Hirschler's positive experiments will have to be in- 

 creased before they can be held against the negative experiments 

 of Jensen, Huxley and Hogben, and myself. 



As to Huxley's and Hogben's positive results 24 on the larvae 

 of Salamander maculosa and triton, quoted by Swingle against 

 me, it should be stated. that the method employed in these experi- 

 ments is such as to permit of no conclusions whatsoever. In the 

 first place, they did not use the first moulting, but the sizes of the 

 gills as an indicator of metamorphosis. The gills may become 

 reduced in size by the action of many factors different from meta- 

 morphosis, particularly by starvation. Since strong iodine solu- 

 tions were used, it is almost certain that contrary to the authors' 

 impression (quantitative measurements of the food intake were 

 not made) the experimental larvae fed less well than the controls. 

 Secondly, nowhere in Huxley's and Hogben's paper can I find 

 any statement indicating the size and stage of the larvae at the 

 beginning of the experiment. Yet if the larvae were in an ad- 

 vanced larval stage any irritation as serious as that caused by 

 iodine solutions would be sure to bring about precocious meta- 

 morphosis. 



24 Huxley. J. S., and Hogben, L. T., Proc. Royal Soc., 1922, XCIII., 36. 



25 Hirschler, J., Arch. Entwcklgsgsmech. d. Orgn., 1922, LI., 482. 



