STERILITY OF HYBRIDS. 409 



one case of the hybrid offspring of two animals, clearly- 

 distinct, being themselves perfectly fertile." 

 On page 327, Origin of Species, he says : 



" The perfect fertility of the many domestic varie- 

 ties differing widely from each other in appearance, for 

 instance those of the Pigeon or (those) of" the cabbage, 

 is a remarkable fact ; more especially when we reflect, 

 how many species there are which though resembling 

 each other most closely, are utterly sterile, when 

 crossed." 



On page 126, Vol. ii, Animals and Plants, &c, he 

 says : 



" The domestic races of both animals and plants, 

 when crossed, are with extremely few exceptions, 

 quite fertile. * *. The offspring, also, raised from 

 such crosses, are likewise generally more vigorous and 

 fertile than their parents. On the other hand, species 

 when crossed, and their hybrid offspring are almost in- 

 variably, in some degree sterile; and here there seems 

 to exist a broad and insuperable distinction (sic) be- 

 tween races and species." 



On page 213, Vol. ii, Animals and Plants, &c, he 

 says that, where species are crossed, "though size is 

 often gained, fertility is lost." 



On page 490 of same volume, he says : 



"There is, however, one important constitutional 

 difference (!) between domestic races and species. I 

 refer to the sterility which almost invariably follows, 

 in a greater or less degree, when species are crossed, 

 and the perfect fertility of the most distinct domestic 

 races, with the exception of very few plants, when 

 similarly crossed. It certainly appears a remarkable 

 fact, that many closely allied species, which in appear- 

 ance differ extremely little, should yield, when united, 

 35* 



