ORIGIN OF MAN AND THE OTHER VERTEBRATES. 613 



rate designation, for it is highly probable that it was from one of the 

 early orders of fishes that the Batrachia took their rise. Omitting from 

 consideration the lowest vertebrata, the sand -lances and lampreys, 

 which are not fishes, we have remaining a body of animals which pre- 



Fig. 3. Skull of Eetofs megacephalus. (Cope.) A Batrachian of the Permian period. One 

 fifth natural size, upper side. (Prom Texas.) 



sent great varieties of structure. Of the four great sub-classes into 

 which they naturally fall, but one can be called true fishes. The others 

 embrace the sharks, the chimaeras, and the lepidosirens. It is interest- 

 ing to note that these four divisions are more closely approximated 

 during the Permian period than at any later time. An order tech- 

 nically referred to the sharks, and known as the Ichthyotomi, com- 

 bines many of the characters found separately in three of the sub- 

 classes. The creatures which especially deserve the name of batrachian 

 fishes, the ceratodonts, etc., also abounded during the Permian period. 

 From this time the true fishes began to run their course. They have 

 peopled all waters, and have branched into a greater diversity of form 



