220 LECTURE VIII. 



races manifest as mucli antipathy to eacli other as so-called 

 species, so that extraordinary circumstances, or the interference 

 of man, is necessary to overcome that antipathy in order to 

 effect the crossing. 



Species, according to Linnaaus, is the corner-stone upon 

 which systematic natural history rests. Linn^us considers 

 species as an originally created form. Buffon, whose opinions 

 oscillated, taught that all individuals which produce a prolific 

 offspring belong to one species, and according as authors at- 

 tached more weight to propagation or classification, the agree- 

 ment in characters, or the production of prolific descendants, 

 became the centre around which the definition turned. Thus 

 Andreas Wagner includes under one species all individuals 

 which produce prolific descendants, without any regard to 

 external characters ; so that the same man who assumed 

 hundreds of species of animals, from niere differences in their 

 fur, would at once include wolf, jackal, and the domestic dog, 

 in the same species, if it could be shown that they produce, in 

 crossing, prolific descendants. Agassiz, on the contrary, 

 rejects prolificacy of offspring as a distinguishing mark of 

 species, which he constructs solely from external characters 

 and their relations to surrounding nature. 



The real cause of such discrepancies must be sought for in 

 the practical treatment of science, and the tendency attributed 

 to it. The reason why some embrace one, and others a dif- 

 ferent theory, is that the results are conflicting if you start 

 from any assumed axiom. Allow me to explain this point. 

 We may boldly assert that, among the many thousand species 

 now known, the number of which will, in the course of time, 

 rise to a million, there are not one hundred whose inbreeding 

 has been traced so far as to enable us to assert that they are 

 infinitely prolific ; we cannot even in the strictest sense assert 

 this of our domestic animals, and still less of wild animals. 

 As regards, therefore, the great majority of species, as Giebel 

 has proved, propagation is purely hypothetical. You will also 

 observe that, in discussions on the establishment of new 

 species, the faculty of propagation is taken into account. 

 Men dispute about the value or worthlessness of distinctive 



