82 THE FIRST PRINCIPLES OF HEREDITY 



IGen. 



as the third generation a complete reversion to one of the 

 grandparents may take place. For instance, if a variety 

 A is crossed with a variety B, both having 16 Idants each, 

 (A being designated by black, B by white, see Fig. 42), 

 then the hybrid (second generation) from both will have a 

 germ-plasm of 8A + 8B ; i.e., it will be intermediate in ap- 

 pearance between both crossed varieties. 



Each germ-cell of this hybrid will, after the reducing 

 division, contain only 8 Idants, and among them must be 



a number of germ- cells 

 with 8 black Idants A. 

 If, now, either inbreed- 

 ing of these hybrids 

 takes place, or crossing 

 with the old parent form 

 A, any such germ-cell 

 containing 8 Idants A 

 may meet with another 

 germ -cell of the same 

 kind, derived either from 

 the hybrid or from the 

 grandparent form A, and 

 thus lead to a germ- 

 plasm containing once 

 more 16 Idants A. This 

 will produce an indi- 

 vidual of the grand- 

 parent type A, though, 

 as we have seen, the 

 hybrid itself was not a replica of the grandparent A, but 

 intermediate between both grandparents A and B. 



While in the crossing of varieties all the Idants could, 

 for practical purposes, be assumed to be identical, express- 

 ing the racial characteristics, in the case of individual traits 

 the Idants would be slightly different in the two parents 

 with regard to detailed individual peculiarities. The ex- 

 planation of the resemblance between grandchild and 



HGen 



BIGen 



FIG. 42. REVERSION. 



