238 CROSSING AND CLOSE-INTERBREEDING. 



with the other parent's positive characters which cor- 

 respond, to effect the development of such characters 

 in the offspring, and a return, full or measurable, as 

 the case may be, to the perfect type. If this power of 

 reversion were not present, there would be no reason, 

 why the defective points of each parent should not, in 

 the offspring, be prepotent, over the positive peculi- 

 arities of the other ; instead of, as is the fact, the posi- 

 tive peculiarities of the one, supplying the deficiencies 

 of the other. It is true, that, under certain unfavora- 

 ble conditions, militating against the operation of re- 

 version, the defects in each or in one, may be, to some 

 degree, prepotent over the positive features in the 

 other. Such a phenomenon, however, is rare. When 

 such is the case, however, there is always to be ob- 

 served an abatement, or absence, of the good, ordina- 

 rily resulting from crossing. This explains the few 

 cases) where, as Darwin shows (with reluctance, be- 

 cause they contravene his law), no good, and even evil, 

 result from a cross. 



Crossing undoes, either wholly, or in a measure, 

 the injury attendant upon a departure from the origi- 

 nal type ; — restores, in a degree, to the offspring the 

 vigor and fertility which defects in development, had, 

 in the parents, destroyed or impaired. It is by the 

 conjunction, in the offspring, of the positive characters 

 in which either parent differs from the other, that the 

 good is effected. It is not the mere addition of struc- 

 tural parts, but the consequent, improved physiology, 

 which secures the benefit from a cross. 



Darwin says (p. 142, Vol. ii, Animals and Plants, &c.)\ 



