ii NEOTENIA in 



frogs, toads, &c., breathe as tadpoles, by means of 

 gills, and that after a few weeks the lungs develop 

 and the gills disappear, while the animal becomes an 

 adult, and acquires new characters and organs. But as 

 every one can ascertain, this gill-breathing period may 

 be considerably lengthened under natural or artificial 

 and experimental circumstances. I have myself kept 

 toads in the tadpole state for over two years, merely 

 by feeding them very scantily. They were born in 

 the spring of 1889, and remained all the time in an 

 aquarium in the laboratory, having water enough at 

 their disposal, being always sufficiently provided with 

 aquatic plants, and enjoying heat enough : it cart by 

 no means be said that their evolution was arrested by 

 the cold of winter, as often happens in mountain ponds, 

 when the cold of autumn sets in before the tadpoles 

 have achieved their development, so that they become 

 frogs or toads only in the course of the following 

 year. In the case of my tadpoles, it seemed that the 

 completion of development was due to my imprudent- 

 ly feeding them in the spring of 1891 on the very sub- 

 stantial flesh of their congeners ; and in the course 

 of some three weeks at most, the limbs were evolved, 

 the long tail disappeared gradually, the very colour 

 and appearance of the skin underwent considerable 

 changes, and my superannuated tadpoles became 

 toads at last. This Neotenia has been observed by 



