112 EXPERIMENTAL EVOLUTION LECT. 



many physiologists in different Amphibians. Mile, de 

 Chauvin has reared larvae which were the progeny of 

 Amblystoma, and while some of them became 

 , Amblystoma, others remained Axolotls in con- 

 sequence of being kept in very well aerated water, 

 where the gills had no tendency to atrophy or retro- 

 gression. Similar experiments have been performed 

 by a large number of naturalists on different species 

 of Triton, Salamandra, Pelobates, Alytes, Hyla, Rana, 

 and Rnfo ; and the result is that while there arc 

 Amphibians, such as Salamandra atra, in which the 

 length of the branchial or gill-bearing period is very 

 short, and others, such asfroteus anguineus, and some 

 Tritons and Axolotls, where gills exist normally in 

 adult and even in aged individuals, there exist 

 also a number of Amphibians among which the 

 gill-bearing period, normally short, may be much 

 lengthened. But in Urodela (newts and sala- 

 manders) this lengthening 1 may and does occur 

 without seriously modifying the evolution of the 

 remainder of the body ; and the result is that these 

 tadpoles are sexually mature, while among Anura 

 (frogs and toads) this lengthening interferes with the 

 general development, and sexual maturity does not 

 seem to occur among the tadpoles. New investigations 



are required to ascertain how far this sexual immaturity 



>** 



exists, and to what extent it may be retarded by the 



