STRUCTURE OF THE VERTEBRATES 



51 



and lungs and breathing entirely through the skin. Others re- 

 tain the external gills throughout life. 



Certain of the urodeles remain in the larval condition, reach- 

 ing sexual maturity without metamorphosis. This permanent 



Bufo, a toad 

 (Anura) 



Cryptobranchus (Urodela) 



Fig. 18. Tj^pes of Amphibia. Cryptobranchus and Amphiuma are the 

 largest living American amphibians. The frogs and toads are liighly 



specialized forms. 



