386 FAUNA ANTIQUA SIVALENSIS. 



tecta. But a great atitliority, one of the most profound 

 naturalists of the age, M. Agassiz, after running over a 

 vast field of observations, has arrived at a very different 

 conception of the meaning of ' Species.' He states his 

 opinion to be, 'that no so-termed character, that is, no 

 observable mark can be so striking as to indicate an absolute 

 specific distinction ; but at the same time it should never be 

 regarded as so trifling as to point to absolute identity ; that 

 characters do not mark off species, but that the combined 

 relations to the external world in all circumstances do.' He 

 believes that he can show ' that many organic beings are 

 specifically distinct, or at least that they stand in no genea- 

 logical relations to one another, although the individuals are 

 so like as to be confounded.' He farther advances the 

 opinion ' that no species occurs in two geological formations — 

 nay, not even in two different parts of one formation ; ' and he 

 believes ' that hereafter it will become necessary to express 

 the specific difference of organic remains by the circumstances 

 of their occurrence without its being possible to assign distinc- 

 tions to them.' 



If we are to apply this conception of ' Species ' to the fossU 

 it must at once be considered as distinct from Emys tecta, 

 for it comes from a different geological formation, where it 

 is associated with numerous extinct forms. But it is obvious 

 that this part of the statement is nothing more than a 

 begging of the question. The distinctness of the species 

 must first be proved, in every case, on independent grounds 

 before the asserted law regarding the order of their occur- 

 rence can be admitted. And, in regard to the other state- 

 ment, that organic forms may be so like as to be undistin- 

 guishable and yet be specifically distinct, and that no ex- 

 ternal characters can be so marked as to determine specific 

 difference, they seem to imply little short of a sort of I^atural 

 History negation of the universal axiom ' that things which 

 are equal to the same are equal to one another.' M. Agassiz 

 appears to entertain the received opinion among naturalists 

 that common genealogy constitutes the essence of a species, 

 but the quoted expressions would imply that he abandons 

 external characters as the test by which such genealogy is to 

 be judged of. 



But naturalists have no right, in determining the specific 

 nature of an organic form, to take into any account the 

 geological position whence it came, any more than geogra- 

 phical place in regard to existing forms. The species ought 

 to be ascertained from the observable marks which it presents 

 apai't from every extraneous consideration ; the proper order 

 of succession being to apply the result thus arrived at to 



