198 CROSSING AND CLOSE-INTERBREEDING. 



mongrel offspring, a character or characters which the 

 other parent variety lacks. The offspring of a cross, 

 then, possesses two characters, at least, where either of 

 its parents possessed one; and, thereby, either a full, 

 or a measurable return to the original, perfect type, 

 comprising all of the characters of the species, is 

 effected. If a return to the sum of all the characters 

 of the species, should result in physiological good, 

 then a cross does but fulfill the requirements of the 

 theory of Reversion, when the effects of a cross are 

 (what Darwin has established, as unexplained facts 

 merely), viz., increased fertility, and increased constitu- 

 tional vigor. 



If, on the other hand, an individual, wanting in any 

 character, or lacking the full development of any 

 character of its species, is, upon the theory of Rever- 

 sion, to be esteemed physiologically defective, inas- 

 much as it falls short of the full, possible development 

 of its species ; then, it is to be expected that, when 

 such individual is interbred with another, similarly de- 

 fective, the evil entailed by such incomplete, or dispro- 

 portionate development, will, in the offspring, be inten- t 

 sified, and become more manifest. As a fact, such is 

 the case. 



The evil effects of Close-Interbreeding, Darwin con- 

 fesses, are wholly inexplicable upon any theory that 

 he can devise. Yet, the theoiy of Reversion gives 

 them a rational, full and conclusive'explanation. 



Not only are these results of crossing, and of close- 

 interbreeding, wholly unintelligible to Darwin, but he 

 shows, that there is a graduated scale of such results, 



