EXAMPLES OF CONNECTION BETWEEN CLASSES. 61 



ruinate over those of the Fish ; and the Lepidosiren (Fig. 20), 



in which the characters of the 

 two classes are so completely 

 blended, that Zoologists have 

 not yet agreed on which side 

 it should be placed. Again, 

 the genuine Reptiles are 

 closely connected with Fishes 

 by two very remarkable ani- 

 mals, not now existing, the 

 Ichthyosaurus (Fig. 21), and 

 the Plesiosaurus (Fig. 22); 



FIG. 20. I.KriflOSIKKX. 



whose remains abound, in cer- 

 tain rocks, to such an extent as to show that they must have been 



Fro. 21. ICHTHYOSAURUS. 



formerly very numerous. On the other hand, there are certain spe- 

 cies of Fishes (which were more numerous and abundant at for- 



F.-o. 2i2 



mer epochs than at present), in whose structure there is much 

 that reminds us of the Crocodiles ; the swimming-bladder some- 

 what resembling a lung, and the vertebral column and ribs possess- 

 ing many characters in which they approach those of that order 

 of Reptiles. In the Eels, again, we have the form of the Serpent 



