REVIEW OF THE HISTORY OF IJFE. 259 



indications of a transition between the two species. Similar 

 statements may be made witli regard to other moliusks of the 

 Pliocene and Modern periods, and there are even species 

 which extend unchanged from the early Eocene. Nor is it 

 impossible that some modern bivalves of the IJrachiopod 

 group may be scarcely modified descendants even of Palieozoic 

 species. 



Perhaps some of the most remarkable facts in connection 

 with the permanence of species and varietal forms arc those 

 lurnished by that magnificent flora which burst in all its 

 majesty on the American continent in the Cretaceous period, 

 and still survives among us even in some of its specific types. 



say survives; for we have but a remnant of its forms living 

 and comparatively little that is new has probably been added 

 since. Take, for example, the facts stated in Chapter VI 1 1. 

 as to the continuance to the present time of species of plants 

 introduced in the Cretaceous and Eocene, and which thus came 

 in at the very time when the great Mesozoic reptiles were 

 decaying or had just disappeared, and when the placental 

 mammals were being introduced. Some of these plants mu; ^ 

 have propagated themselves unchanged for half a million ot 

 years. 



Plants and the lower tribes of animals are, however more 

 permanent than the higher animals ; and a strange cr,ntrast 

 IS afforded to the foregoing examples of persistence by the 

 repeated revolutions that have affected vertebrate life since 

 the Mesozoic age. Yet even in the case of vertebrates there 

 seems to have been little change, except in the extinction of 

 species, since the Pliocene period. 



In conclusion of this review, r m we formulate a few of the 

 general laws, or perhaps I had better call tlicm the general 

 conclusions respeciu-' life, in which all pahcontologists may 

 agree. Perhaps it is not possible to do this at i)resent satis- 

 factorily, but the attempt may do no harm. We my, then, 

 I think, make llie following affirmations :— 



s 2 



