326 REGENERATION AND NEOTENY 



Though such a difference between two different groups of animals is 

 possible, it does not seem likely that metamorphosis should be con- 

 trolled in different groups of amphibians by mechanisms so different; 

 at least such an assumption does not seem justified by the evidence 

 presented in Kammerer's paper. In the first place, that which 

 Kammerer calls neoteny in his Triton larvae is, as far as his recorded 

 data are concerned, only a difference of 1 month. In one instance 

 the operated animals transformed 1 month later than the controls; 

 in the second experiment the operated larvae had not metamorphosed 

 14 days after the controls had completed metamorphosis; at this time 

 the experiments were discontinued.^ Nowhere do we find any indica- 

 tion that the sex organs were actually examined to make sure that 

 they had developed at a more rapid rate than the rest of the organism. 

 Nor do we find any proof that these small differences had not been 

 produced merely by differences in the quantity of food or that they 

 were not due to the fact that the larvae of the different sets were the 

 offspring of different females. Since the same objections could be 

 raised with regard to his experiments on tadpoles, it becomes doubtful 

 not only that so fundamental a difference exists between Caudata and 

 Salientia as that claimed by him, but also whether amputation and 

 regeneration had any effect on the metamorphosis of Kammerer's 

 larvae at all. In a later article^ he emphasized the fact that the 

 retardation of metamorphosis in his larvae was not due to a retarda- 

 tion of growth because of insufficient food ; he says : 



"Individuals particularly suited for the production of the phenomena of neo- 

 teny are those which have been subjected to experiments on regeneration, since 

 they as a rule retain . . . for a long time after the removed parts have 

 been replaced the larval condition without showing any particular inhibition of 

 the general growth of the body; hence they turn into truly neotenous, not into 

 starved larvae!"^ 



It is in this case of course extremely difficult to form any opinion 

 about the causes which lead to retarded metamorphosis, since appar- 

 ently these animals were well fed, but it is well known, and we have 



* Kammerer, P., Arch. Entwcklngsmechn. Organ., 1904, xvii, Experiment XI, p. 

 167, and Experiment XII, p. 168. 



^ Kammerer, P., Arch. Entwcklngsmechn. Organ., 1904, xvii, 165. 

 ^ Kammerer, P., Arch. Entwcklngsmechn. Organ., 1904, xvii, 240. 



