STERILITY OP HYBRIDS. 423 



such limit precludes the possibility of the evolution 

 of "permanent races," into distinct species. Huxley 

 says; that Darwin starts with an incontestable assump- 

 tion, viz., " the existence of living matter endowed with 

 variability." Incontestable it is ; but, Darwin essays, at 

 the next stage in his argument, an assumption which is 

 contestable, viz. : General ignorance of the law of such 

 variability; and the absence, therefore, of any law for- 

 bidding his next gratuitous assumption, that variability 

 is unlimited. This assumption is not tenable, for, (i) 

 there is a law governing variability, and (2) such law 

 completely imposes a limit to positive variations, while 

 (3) the law of proportionate development imposes a 

 limit to negative variations. All variability, of a positive 

 character, is limited to the regain of characters, once 

 lost by the species ; and variability, of a negative char- 

 acter, is confined within a narrow range in each species, 

 by the sterility and extinction which await the loss of 

 a given number of the organs and features of such 

 species. 



The cause of the sterility, and of the lessened fer- 

 tility, among individuals of a variety deficient in fea- 

 tures of its species, is, that there are not sufficient char- 

 acters in those individuals, to impress their reproduc- 

 tive tissue with due, formative power. The reason of 

 the sterility of hybrids, is because the hybrid is 

 formed of characters belonging to two different spe- 

 cies, and, therefore, the result of the coordination of 

 the characters of the organism is not directed to the 

 required point. The influence of the aggregate is not 

 centered upon that tissue which is specially prepared 



