S24 THE LNDUCnONB OF BIOLOGY. 



est times geologically recorded, down to onr own time ; and we 

 have no visible evidence of superiority in tlie existing genera 

 of these orders. In Ms lecture " On the Persistent Types of 

 Animal Life," Prof. Huxley enumerates many cases. On 

 the authority of Dr. Hooker, he stated " tliat there are Carbon- 

 iferous plants which appear to be generically identical with 

 some now living ; that the cone of the Oolitic Araucaria is 

 hardily distinguishable from that of an existing species ; that a 

 true Pinus appears in the Purbecks and a Juglans in the 

 chalk." Among animals he named palaeozoic and mesozoic 

 corals which are very like certain extant corals ; genera of Silu- 

 rian molluscs that answer to existing genera; insects and arach- 

 nids in the coal formations, that are not more than generically 

 different from some of om* own insects and arachnids. He 

 instanced " the Devonian and Carboniferous PleuTacaiithus^ 

 which differs no more from existing sharks than these do 

 from one another ; " early mesozoic reptiles " identical in the 

 essential characters of their organization with those now liv- 

 i]ig ; " and Triassic mammals which did not differ " nearly so 

 much from some of those which now live, as these differ from 

 one another." Continuing the argument in his " Anniversary 

 Address to the Geological Society " in 1862, Prof. Huxley 

 gave many cases in which the changes that have taken place, 

 are not changes towards a more specialized or higher organ- 

 ization — asking '' in what sense are the Liassic Chelonia infe- 

 rior to those wbicli now exist ? How are the Cretaceous 

 Ichthyosauria, Plesiosauria, or Pterosauria less embryonic 

 or more differentiated species than those of the Lias ? " 

 While, however, contending that in most instances " positive 

 evidence fails to demonstrate any sort of progressive moditi- 

 cation towards a less embryonic or less generalized type in a 

 great many groups of animals of long-continued geological 

 existence ; " Prof. Huxley added, that there are other groups 

 " co-existing with them, under the same conditions, in which 

 more or less distinct indications of such a process seem to be 

 traceable." And in illustration of this, he named that better 



