260 ZOOLOGY 



purplish spots on the sides. Both Spelerpes and Desmo- 

 gnathus live in and about running brooks, under stones 

 and fallen logs. Their eggs are attached to the under 

 surface of submerged stones. The adults are easy to keep 

 in confinement in a moist fernery. They may be obtained 

 out of doors all the year round, excepting during the time of 

 deep snow. There are four species of Spelerpes and three 

 species of Desmognathus in the northern United States. 



Metamorphosis. As we have seen, all Amphibia have 

 gills while young, but some lose them before maturity 

 while others retain them permanently. Those species 

 which retain the gills pass their whole life in water ; the 

 others may live on the land. The loss of gills is asso- 

 ciated with the assumption of a land life. In the Ambly- 

 stoma we have species which are curiously intermediate 

 between the two classes in that they may retain their 

 gills, tail-fins, and other structures adapted to aquatic life, 1 

 even to the time of reproduction ; or they may lose their 

 gills and tail-fins. The first result follows if they are pre- 

 vented from coming on land ; the second, if they are forced 

 to leave the water. The capacity of the Mexican Axolotl 

 for either becoming an adult or remaining a larva was 

 first shown by some experiments of the German naturalist 

 Weismann and a pupil of his. It will be seen that when 

 forced to live in the water Axolotl retains permanently 

 a larval condition ; and one would never know that in this 

 larval condition the animal is not adult were it not for the 

 accident of its sometimes becoming adult. It is quite 

 possible that all of the Urodela which retain their gills 

 throughout life may formerly have had a gill-less adult 

 stage which is now lost. 



1 Compare Fig. 243. 



