APPEARANCE OF VERTEBRATE ANIMALS. 131 



dominant, or is developed to the exclusion of the others (Figs 

 118, 119). 



The Ganoids and Dipnoi still, however, occupy a very im- 

 portant place through the Mesozoic ages (Fig. 120), and it 

 is only at the close of the Cretaceous that they finally give 

 place to the Teleosts, or common fishes, which, though perhaps 

 more fully specialised in purely ichthyic features, have dropped 

 the reptilian characteristics of 

 their predecessors (Fig. 121). 

 It is interesting to observe that 

 these old-fashioned fishes had 

 culminated before the advent of 

 air-breathing Vertebrates, which 

 appear for the first time in the 

 Carboniferous, li is further to 

 be observed that groups of fishes 

 furnished wit'.i means of aiding 

 their gills by rudimentary lungs 

 were especially suited to waters 

 more charged with carbonic acid, 

 and less with free oxygen, than 

 those of more recent times. 

 This remark especially applies 

 to the mephitic and sluggish 

 streams aid lagoons of the 

 Carboniferous swamps, where. 



m 



the midst of a rank Vege- Fir.. 1 18.— Teeth of Cretaceous Sharks 

 , , . . iptodits s.nd Ftyc/wdus). — After Leidy. 



tation and reeking masses of 



decaying organic matter, the half air-breathing fishes and tie 

 amphibious reptilian animals met vith each other and found 

 equally congenial abodes. Thus, independently of the fact that 

 some of these fishes were probably vegetable feeders, it is not 

 altogether an accident, but .a wise adaptation, that caused the 

 culmination of the reptilian fishes and batrachian reptiles to 

 coincide with the enormous development of the lower forms 



