316 Experimental Zoology 



were first well fed so that they might be strong enough to pass 

 through the period of metamorphosis during which they take 

 no food ; for if in poor condition they die before the transforma- 

 tion is completed. They were then put into shallow water, or on 

 a moist surface, and in the course of one to three weeks, or 

 longer, the change took place. The skin loses its sliminess, 

 the dorsal fin disappears, the tail loses its broad border, and the 

 gill slits close. The change appears to be connected with the 

 enforced respiration by means of lungs instead of gills ; possibly 

 the drying of the skin may be a factor in the result. 



Shuf eldt 1 has given a very complete account of the metamor- 

 phosis of Amblystoma tigrinum in New Mexico. He finds that 

 axolotls change into Amblystomas more readily if kept in water 

 containing little air. If the transformation is induced to a cer- 

 tain point,' the animal will complete it without further stimulus. 

 Young axolotls are more easily made to transform than are older 

 individuals. The metamorphosis is hastened by regularly sup- 

 plying the animals with an abundance of food, "and what is 

 still more interesting, when they are thus treated it markedly 

 affects the appearance of the transformed Amblystomas." If 

 \vell fed on meat the Amblystomas are not only larger, but of a 

 deep black color without spots, while those not well fed are 

 mottled with bright yellow and pale brown. The depth of the 

 water seems to have "a wonderful influence" upon the meta- 

 morphosis ; the deeper the water, the slower the metamorphosis. 2 

 A moderate increase in temperature seems to hasten the trans- 

 formation. In the same pond in process of drying up all stages 

 in the metamorphosis may be found, animals caught in 

 shallower parts undergoing a rapid transformation; those in 

 deeper parts being unchanged. 



Neotenia has also been observed in the tadpoles of frogs, but 

 to a less degree, since they do not reach sexual maturity in this 

 form. Certain organs, only, advance in their development, while 

 others remain at an earlier stage. If the transformation of the 



1 Science, September, 1885, p. 263. 



2 This may possibly be due to the diminished chance of using the lungs. 



