412 LECTURE XIV. 



influences^ and partly by artificial breedings new well charac- 

 terised races and species may arise admits of no doubt. In th'e 

 raceless animals of tbe first category wbicli are produced by 

 transplantation into other regions^ that formative process takes 

 place which we have just characterised and by which a fixed 

 type is gradually produced corresponding to the altered con- 

 ditions. In so-called degenerate animals, which by want of 

 care approach the original form, this racelessness must cease 

 when the relapsing process attains its limits ; so that of 

 the three cases established by Nathusius two have only a 

 temporary limited value, whilst the third — the racelessness 

 produced by the crossing of different races, is more generally 

 applicable. 



Let us now examine more closely this point concerning 

 mongrels and hybrids, for which purpose we must return to 

 the terms " variety and species." 



Every naturalist who has critically examined the question of 

 species has arrived at the conviction, that the conception of 

 species does not always consist in a definite sum of distinctive 

 characters ; but that, on the contrary, in each group both the 

 sum of the characters as well as the chief characters difier es- 

 sentially. We possess genera in which every species has as 

 sharply incised characters as an antique gei;n ; there are others 

 (especially genera with many species) in which the species as it 

 were coalesce, and can only with diflSculty be distinguished, 

 frequently grouping themselves around a centre, so that within 

 one genus several principal species arise, around which other 

 species place themselves. These groups of allied species arise 

 by their possessing some chief character in common, whilst some 

 other characters may difi'er in alhed species. The sum of the 

 distinctive characters, as well as their quality, has in every 

 type we examine its particular laws, which cannot be generally 

 formalised. But we have seen that both quality and sum of 

 distinctive characters may in difierent races be as great and 

 even greater than in dilFerent species. The characters can 

 thus only serve for determining the races, when we admit that 

 race and species are identical, and inseparable conceptions. 



But we are told : Species have persisted since times imme- 



