I'TilLOSOrilY OF ZOOLOGY. 



place among individuals of nearly related species. Thus, 

 among quadrupeds, the mule is the produce of the union 

 of the horse and the ass. The jackall and the wolf both 

 breed with the dog. Among birds, the canary and gold- 

 finch breed together, the Muscovy and common duck, and 

 the pheasant and hen. Among fishes, the carp has been 

 known to breed with the tench, the crusian, and even the 

 trout *. 



2. The Parents must be in a confined or domesticated 

 state. In all those hybridous productions which have yet 

 been obtained, there is no example of individuals of one 

 species giving a sexual preference to those of another. 

 Among quadrupeds and birds, those individuals of different 

 species which have united, hare been confined, and exclud- 

 ed from all intercourse with those of their own kind. In 

 the case of hybridous fishes, the ponds in which they have 

 been produced have been small and overstocked, and no 

 natural proportion observed between the males and females 

 of the different kinds. As the impregnating fluid, in such 

 situations, is spread over the eggs after exclusion, a portion 

 of it belonging to one species may have come in contact 

 with the unimpregnated eggs of another species, by the ac- 

 cidental movements of the water, and not in consequence 

 of any unnatural effort. 



In all cases of this unnatural union among birds or qua- 

 drupeds, a considerable degree of aversion is always exhibit- 

 ed, a circumstance which never occurs among individuals 

 of the same species (. 



Phil. Trans. 1771, p. 318. 



JOHN HUNTER having succeeded in producing a breed between the 

 dog and the wolf and jackall, hastily concluded that they all belonged to the 

 species, by overlooking the aversion to the intercourse which was exhibited. 

 Phil. Trans. 1787, p. 253. and 1789, p. 160. 



