1 76 PALAEONTOLOGY. 



two genera to the air bladder and duct, as being of a more 

 reptilian character than the corresponding parts would present 

 in most other fishes. But the palaeontologist would point to 

 the persistent noto chord, and to the heterocercal tail in 

 palaeozoic and many mezozoic fishes, as evidence of an " arrest 

 of development," or of a retention of embryonic characters in 

 those primaeval fishes. 



One other conclusion may be drawn from a retrospect of 

 the mutations in the forms of the fishes at different epochs of 

 the earth's history, — viz., that those species, such as the 

 nutritious cod, the savoury herring, the rich-flavoured salmon, 

 and the succulent turbot, have greatly predominated at the 

 period immediately preceding and accompanying the advent 

 of man ; and that they have superseded species which, to 

 judge by the gristly sharks and bony Garpikes (Lepidoste-us), 

 were much less fitted to afford mankind a sapid and whole- 

 some food. 



ICHJSTOLOGY* 



In entering upon the genetic history of the class of 

 reptiles, we have to inquire, as in that of fishes, at what period 

 of the earth's history the class was introduced, and under 

 what forms ; at what period it attained its plenary develop- 

 ment, in regard to the size, grade of structure, number and 

 diversities of its representatives ; and the relations which 

 the existing members of the class bear to its past condition. 

 Fifteen years ago, the oldest known reptilian remains were 

 those of the so-called " Thuringian Monitor," from the Permian 

 copper-slates of Germany. Since that time the batrachian 

 Apateon, or Arclugosaurus has been discovered in a Bavarian 

 coal-field ; and footprints in carboniferous sandstones of 

 North America have borne testimony to the fact, if not the 



* G-r., Ichnos a footstep, logos a discourse. 



