THE FORMATION OP VARIETIES. 193 



upon their modification of such mould, abate. It is evi- 

 dent, upon Darwin's own showing of the manner in which 

 varieties of a species are formed, that each variety, when 

 not distinguished from the others of the same species, 

 merely by a negative character, has in it an element, 

 which, if joined to another variety, would measurably 

 advance the development, of such other variety, towards 

 the original type or mould of the given species ; and, 

 that the combination of all the positive characters of 

 many and widely distinct varieties of a species, in a 

 single, or in each, individual, would realize the true 

 mould, which is the sum of all the positive develop- 

 ments, possible in such species. 



17* 



