12 DARWIN'S THEORY. 



the goose, the turkey, the hive-bee, &c, have not 

 developed features, in their individuals, sufficiently 

 marked and varied, to serve as the foundation of any 

 very distinct varieties, a multitude of other species dis- 

 play modifications which form the distinguishing char- 

 acters of very widely divergent breeds. Many of the 

 modifications, or improvements, which have arisen 

 under man's care, and which were not known to the 

 species, when taken from the state of nature, have led 

 to the formation of varieties, in such species, with dis- 

 tributed differences distinguishing them, greater even 

 than those differences which distinguish one species 

 from another ; and, in some cases, greater even than 

 those which mark one genus from another. 



The distinction between species and varieties, should 

 be thoroughly appreciated, by the reader, that he may 

 understand Darwin's argument. A species is gener- 

 ally taken to be, that class of organisms which are 

 known to have a common descent from some ancient 

 progenitor, and which are capable of indefinitely- 

 continued, fertile reproduction among each other ; but 

 which, on being crossed with individuals of another 

 species, ' are either sterile, or give birth to offspring, 

 called hybrids, which are sterile. Thus, a horse, and 

 an ass, are taken to be distinct species. A mule, how- 

 ever, is a hybrid — being the result of a cross between 

 the two species — and, as is well known, is sterile. A 

 variety, or breed, on the other hand, is one of a class 

 of organisms, within a species, distinguished from its 

 fellow varieties of the same species, by the possession 

 of some peculiar, negative or positive character ; and 



