408 THE INDUCTIONS OP BIOLOGY. 



his lecture " On the Persistent Types of Animal Life," Prof. 

 Huxley enumerated many cases. On the authority of Dr. 

 Hooker he stated " that there are Carboniferous plants which 

 appear to be generically identical with some now living : that 

 the cone of the Oolitic Araucaria is hardly 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 Silurian molluscs that answer 

 to existing genera; insects and arachnids in the coal-forma- 

 tions that are not more than generically distinct from some of 

 our own insects and arachnids. He instanced " the Devonian 

 and Carboniferous Pleuracanthus, 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 living ; " and Triassic mammals 

 which did not differ " nearly so much from some of those 

 which now live, as these differ from one another." Continu- 

 ing 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 organization asking 

 "in what sense are the Liassic Chelonia inferior to those 

 which now exist? How are the Cretaceous Ichthyosauria, 

 Plesiosauria, or Pterosauria less embryonic or more differenti- 

 ated species than those of the Lias ? " While, however, con- 

 tending that in most instances "positive evidence fails to 

 demonstrate any sort of progressive modification 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 development 

 of the vertebra? which characterizes some of the more 

 modern fishes and reptiles, when compared with ancient fishes 



