90 OUR REPTILES. 



nerves, bones, and blood-vessels atrophy, and vanish from our 

 sight. They have not faded away, they have not simply fallen 

 off, they have not been cast off by a species of moulting, as in 

 the case of insect larvas. They have been got rid of by none of 

 these methods ; their substance has been re-absorbed, atom by 

 atom ; and hence, although it has ceased to exist, it is not the 

 less alive on that account. 



We see, then, that frogs undergo complete metamorphoses, 

 not only in regard to their entire organism, but as to each set of 

 apparatus, with the exception of the nervous system. The sala- 

 manders are not similarly situated. These maintain their 

 external gills throughout the entire larval period, and never 

 acquire internal branchiae. When reaching the air-breathing 

 condition, they skip as it were, one of the transformations which 

 frogs undergo. The salamanders have also four legs in a perfect 

 state ; but then, in addition to these, they preserve the tail * 



* "Metamorphosis of Man and the Lower Animals." Trans- 

 lated by Dr. Lawsen. London : Hardwicke. 



