216 AMPHIBIA 



of life and then take place, but if the history of each generation 

 has some hereditary influence on the next the neoteny itself 

 would become hereditary until, after many generations, the 

 metamorphosis would not take place at all and we should have 

 the larval, that is to say, the gill-breathing stage, lasting 

 throughout life as in the axolotl. At the same time the ori- 

 ginal hereditary tendency to the metamorphosis would not be 

 entirely lost, but only latent, and thus when the original condi- 

 tions to which the metamorphosis is related were restored, the 

 metamorphosis would take place as it does in the axolotl. The 

 conditions which produce neoteny affect the respiratory organs 

 and there is no reason why they should prevent the develop- 

 ment of the reproductive system ; therefore the fact that the 

 persistent larvae may become sexually mature requires no 

 special explanation, especially in view of the fact that the 

 reproduction of the normal adult form takes place in the 

 water. 



It has been urged as one of the difficulties in explaining 

 neoteny by the influence of conditions that in a number of 

 larvae living under the same conditions, whether in nature or in 

 captivity, some are found to remain in the larval stage while 

 others go through the metamorphosis in the normal manner. 

 This fact, however, does not constitute any insuperable objec- 

 tion to the explanation offered above. In the first place this 

 irregularity in the results did not occur in the experiments of 

 Marie von Chauvin on the axolotl ; she was able to cause the 

 animals to change into Amblystoma or to remain in the condi- 

 tion of Axolotls as she pleased. In the second place when 

 numerous larvae live in nature in a large body of water well 

 supplied with oxygen, it is impossible to say that they have all 

 been exactly under the same conditions, for it will be to some 

 extent a matter of chance whether a given specimen rises to 

 the surface and takes air more often than another, and although 

 the larvae are living together the amount of stimulus applied to 

 lungs or gills by free oxygen on the one hand or dissolved 

 oxygen on the other, will differ greatly in different specimens. 

 Lastly it must be remembered that individual differences occur 

 in all animals in all characters, and therefore doubtless occur in 

 the strength of the tendency to metamorphosis in Amphibian 

 larvae. There is no evidence, however, that any individual is 



