SPECIES. 251 



unprejudiced naturalist who in our days would dare to 

 maintain: 1st, that it is proved that all the domesticated 

 varieties of sheep, of goats, of bulls, of llamas, of horses, 

 of dogs, of fowls, etc., are respectively derived from one 

 common stock; 2nd, that the supposition that these 

 varieties have originated from the complete amalgamation 

 of several primitively distinct species is out of the ques- 

 tion ; and 3rd, that varieties imported from distant coun- 

 tries and not before brought together, such as the Shanghae 

 fowl, for instance, do not completely mingle'? Where is 

 the physiologist who can conscientiously affirm that the 

 limits of the fertility between distinct species are ascer- 

 tained with sufficient accuracy to make it a test of specific 

 identity? And who can say that the distinctive charac- 

 ters of fertile hybrids and of unmixed breeds are suffi- 

 ciently obvious to enable anybody to point out the primi- 

 tive features of all our domesticated animals, or of all our 

 cultivated plants'? As long as this cannot be done, as 

 long as the common origin of all races of men, and of the 

 different animals and plants mentioned above, is not 

 proved, while their fertility with one another is a fact 

 which has been daily demonstrated for thousands of 

 years ; as long as large numbers of animals are her- 

 maphrodites, never requiring a connection with other 

 individuals to multiply their species; as long as there are 

 others w T hich multiply in various ways without sexual 

 intercourse, it is not justifiable to assume that those 

 animals and plants are unmixed species, and that sexual 

 fecundity is the criterion of specific identity. Moreover, 

 this test can hardly ever have any practical value in most 

 cases of the highest scientific interest. It is never re- 

 sorted to, and, as far as I know, has never been applied 

 with satisfactory results to settle any doubtful case. It 



