PALEONTOLOGY 71 



a large scale, although it may be imperfect in details. 

 We have not discovered the first bird or crab, or the 

 first fish, but we have discovered the order of their 

 first appearance. 



The following may, I think, be considered as the 

 principal generalisations of palaeontology, founded 

 on good evidence. 



1. Extinct animals and plants were constructed 

 on the same plans of organisation as living ones. 

 We infer this from the hard parts which have been 

 preserved. In shells and bones we find marks of the 

 former attachment of muscles in the same places 

 where muscles are now attached to somewhat similar 

 bones and shells ; and we cannot resist the conclusion 

 that both extinct and living species had similar 

 muscular systems. Some extinct mammals have 

 sharp cutting teeth , others have flat bruising teeth ; 

 the one evidently adapted for catching and eating 

 animals, the other for grinding down vegetable food. 

 Consequently we must infer that the ancient Carni- 

 vora had an alimentary system fitted for digesting 

 flesh , while the Herbivora had one fitted for digesting 

 vegetable food. Their alimentary systems may not 

 have been so well developed as in living animals, 

 but they must have been formed on the same types. 

 So in extinct bivalve shells we find some with and 

 some without a pallial-sinus, and we infer with cer- 

 tainty that those shewing the sinus had long siphons. 

 Also we find that some of the shells of ancient Gas- 

 teropods had round apertures, while others are 

 notched or else drawn out into a canal. Both kinds 

 are still living and of these the round mouthed forms 



