INTERBREEDING OF THE TWO RACES. 87 



denote a group of animals which can breed freely 

 amongst, themselves, but which, if united with animals 

 of another appearance, will not produce fertile cross- 

 breeds with them ; that is to say, they will not pro- 

 duce young which can go on indefinitely producing 

 amongst themselves a race of cross-breeds as freely 

 as either set of parent animals would have gone on 

 reproducing forms like themselves. Creatures which 

 are in this way restricted are physiological species." 

 And in his 'Genesis of Species,' p. 2, he says: — 

 " 'J'he word species denotes a peculiar congeries of 

 characters, innate powers and qualities, and a certain 

 nature realized indeed in individuals, but haviug no 

 separate existence, except ideally, as a thought in 

 some mind." 



Dakwin (' On the Origin of Species,' p. 52) says : — 

 " I look at the term species as one arbitrarily given 

 for the sake of convenience to a set of individuals, 

 closely resembling each other, and that it does not 

 essentially diflTer from the term variety, which is 

 given to less distinct and more fluctuating forms. 

 The term variety, again, in comparison to mere indi- 

 vidual differences, is also applied arbitrarily, and for 

 mere convenience' sake." 



Darwin (' Animals and Plants under Domesti- 

 cation,' vol. i. p. 46 et seq.) gives numerous instances 

 of Wild Cats of this and other countries interbreed- 

 ing with the Domestic Cat. 



Sir W. Jardine (' The Naturalist's Library,' vol. ii.) 

 gays : — " We have no doubt that since its introduc- 

 tion to this country (that is, the Domestic Cat), and 

 more particularly to the north of Scotland, there lias 

 been occasional crossing with our own native species, 

 and that the result of these crosses has been kept 



