FISH-LIZARDS. 87 



that the Fish-Lizards would have continued to breathe 

 air by means of gills, after the manner of fishes. 

 And it is, therefore, considered probable that these 

 saurians are the descendants of still earlier land rep- 

 tiles ; in which respect they again present another re- 

 semblance to Whales, which appear to have been 

 derived from land animals probably more or less nearly 

 allied to the hoofed mammals. If, now, we look back 

 and endeavour to fix upon the ancestral type of crea- 

 ture from which the Fish-Lizards have probably been 

 derived, we are led to select the Primeval Salamanders 

 described in the fourth chapter as the most likely 

 claimants to this position. In treating of that group 

 we have mentioned the peculiar labyrinth-like internal 

 structure of their teeth, from which the name of Labyrin- 

 thodonts has been derived. Now it is very suggestive 

 that the teeth of most species of Fish-Lizards retain 

 traces of this very remarkable labyrinthic structure ; 

 and since, moreover, the skulls of these saurians have 

 certain peculiar features also found in those of the 

 Labyrinthodonts, while the structure of the backbone 

 is very similar in the two groups, it seems highly pro- 

 bable that the Fish-Lizards have been directly derived 

 from ancient reptiles more or less closely allied to the 

 Labyrinthodonts, if not from that group itself; and 

 that as they gradually became more completely aqua- 

 tic their limbs were developed into the very complex 

 paddles of the typical forms. 



In conclusion, we have already pointed out several 

 remarkable resemblances between the ancient Fish- 



