26o 



THE DOCTRINE OF DESCENT. 



breathing; the systematic series from the proteus to 

 the triton and the salamander, likewise exhibits this 

 physiological ascent, linked with various morphological 

 transformations, which may similarly be shown between 

 the ancient and modern specimens of the Labyrintho- 

 donts. The Batrachians, indeed, rise higher in develop- 

 ment than the Coecilia; but, as the friend above men- 

 tioned informs me, they more nearly approach the 

 Myxine in the construction of the internal gills of their 

 larva. We shall obtain a general view of the reptiles by 

 means of the appended diagram, in which we shall avoid 

 any minute systematic designations. 



e 

 o 



Present Age 



Diluvium 



Tertiary Period 



Clialk 



Oolite 



Trias 



Dyas 



Coal 



t 

 t 



t 

 T 



