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THE AMERICAN NATURALIST [Vol. LVI 



ger '13), salicylic acid injections (Kaufman '18), iodine 

 and iodoform injections (Hrischler '18- '19), organic io- 

 dine feeding— iodothyrosine, also injections of iodocasein, 

 iodoserumglobulin and iodoserumalbumin (Jensen '21); 

 and of course Marie von Chauvin's experiments are well 

 known. 



It is evident that the peculiar thyroid inhibition caus- 

 ing neoteny in axolotl is due to genetic factors and that 

 the condition is hereditarily transmitted. It is interest- 

 ing to note that in axolotl we have one of the best ex- 

 amples of hereditary transmission of an endocrine defect 

 known. Attempts to explain neoteny by assuming that 

 environmental agencies such as cold, altitude and the like 

 are the chief causative factors are too crude to be seri- 

 ously considered and for this reason— the aquarium deal- 

 ers of Europe breed their animals as larvae and the young 

 grow up as axolotls, the matter of cold or altitude not en- 

 tering into the question. As was previously mentioned, 

 the European strain arose from a few animals taken to 

 France in 1863. 



Then, too, both Professor Laurens and myself received 

 our animals from Albuquerque, New Mexico, where they 

 breed. The animals were old when captured. The tem- 

 perature of the pools in the vicinity of the city can not 

 be very low even in winter— not nearly so cold as those 

 of the middle western states, northern New York, Ohio, 

 or Wisconsin— and axolotls have never been reported as 

 occurring in these states so far as the writer is aware. 



The Amhlystoma tigrinum resulting from the meta- 

 morphosis of the axolotls during my experiments were 

 placed in certain pools in the vicinity of New Haven 

 where other s|)epi('s of Ainhhisfowa -avo kiunvn to breed. 

 The animals aiv full -rou n and sii,.uM brrcl next spring 

 (1923). By n.llowino- tlif life history of tli.- larva' it is 

 hoped that sonic new light may ])e shed upon the obscure 

 and nuich dohato.l problem of the relation of neoteny to 



