STERILITY OP HYBRIDS. 413 



ferences in the quantity of these good effects, which 

 Darwin similarly accounts as phenomena the cause of 

 which " no fellow can find out," are due to the differ- 

 ent degrees, in which each such pair of varieties, con- 

 tribute characters to such offspring. There is no 

 phase of sterility, or of fertility, which is not suscepti- 

 ble of clear explanation, by means of the theoiy of 

 reversion. 



Therefore : his argument of an appeal to other 

 things of which we are assumed to be ignorant, must 

 fall to the ground, when it is found that we are not 

 ignorant of those things. We shall show below, that 

 this appeal of his, to the different degrees of fertility 

 and of sterility, with individuals of the same species, 

 instead of getting him out of one difficulty, only causes 

 him to put his foot into another, infinitely worse. The 

 explanation of those things of which he assumes we 

 are ignorant, is replete with disproofs stronger, by far, 

 than is even the fact of the sterility of hybrids. • 



2. It is on page 330, of his Origin of Species, that he 

 advances his other argument, viz., That the sterility of 

 species, and of their hybrid offspring, is not " a special 

 endowment," but has been slowly acquired. He there 

 repeats his argument from ignorance, and adds his 

 second reason why the objection, founded on sterility 

 of hybrids, should not obtain. He says : 



"The general fertility of varieties, considering how 

 entirely ignorant we are on the causes of both fertility 

 and sterility, does not seem to me sufficient to over- 

 throw the view taken" (by himself) "that the invaria- 

 ble 'sterility of first crosses between species, and of 



