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. 
Shufeldt’ 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 
well 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.” 
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 
' Science, September, 1885, p. 263. 
* This may possibly be due to the diminished chance of using the lungs. 
