THE PHENOMENA OF REVERSION 305 



species of which ;ths is represented, although the individual 

 specimens still display considerable ditTerences in form/ * The 

 result of these observations also agrees with our theory, for even 

 in the second generation of hybrids, eight was the highest pos- 

 sible number of ids of the ancestral species A in the mature 

 serm-cells of the hvbrid, and in the process of fertilisation these 

 met with the same number of idants of the ancestral species B, 

 which was used for recrossing. The germ-mother-cells of the 

 f hybrid cannot contain more than 8A x 8B, and, as a rule, a 

 smaller number of the idants of A will be present. The reducing 

 division then again halves these sixteen idants in various ways ; 

 and in the case which is most favourable for the preservation of 

 the hereditary substance of A, the halving of one of these germ- 

 mother-cells, which was most favourable for A, might again lead 

 to the formation of germ-cells with eight idants of A and eight 

 of B. But in all other i| hybrids the germ-mother-cells already 

 contain more idants of B than of A, as is shown in Fig. 22, III., 

 and the reduction therefore results in the germ-cells containing 

 either idants of B only, or, at any rate, some of B in addition 

 to those of A. If these egg-cells are then fertilised by germ- 

 cells of the pure ancestral form B, the largest conceivable 

 number of idants of A which can be contained in' the fertilised 

 egg-cell will again be eight. Hence the form exactly inter- 

 mediate between the two ancestors may possibly also appear in 

 the third generation, but this will occur Jiiuch more rarely than 

 in the second generation. On the other hand, those individ- 

 uals the idioplasm of which contains only a few idants of A 

 will preponderate ; and in others, even idants of B only may 

 be present, for the idants of B were in the majority in most of 

 the mother-germ-cells of the second generation : the halving 

 due to the reduction must therefore have frequently resulted in 

 the distribution of idants of B only to one of the germ-cells, and 

 these then once more combined in the third generation with 

 idants of the pure species B. Theoretically, therefore, the 

 \ hybrids must in part revert to the ancestral form B. This 

 conclusion is supported by facts, inasmuch as Kolreutter and 

 Gartner, who made a large number of experiments on recross- 

 ing, found ' that three to six generations (four to five as a 

 rule) were required for the complete transformation of the 



* Focke, p. 485. 



