THE PHENOMENA OF REVERSION 313 



as regards the greaf -grandparent. Instances of a descendant 

 of an ancient family reverting to a great-grandparent whose 

 characteristics were not present in the intermediate generations, 

 are certainly occasionally mentioned in novels, but it is only 

 natural to doubt the accuracy of such cases, even when they 

 claim to be true. A great-grandchild certainly often resembles 

 its great-grandparent, but when this is so, tliis resemblance had 

 not disappeared entirely in the ijitermediate generations. As has 

 been shown above, it would certainly not be incredible, from 

 a theoretical point of view, that the group of idants which con- 

 trolled the development ot the great-grandparent should remain 

 intact in certain germ-cells of two generations, and should be 

 suppressed by more powerful groups derived from germ-cells of 

 other parents, once more to predominate in the third generation. 

 If reversion of this kind could be proved to occur, it might be 

 explained in this manner, and we should be justified in assuming 

 that in many cases the idants of the two parents may again be 

 separated into their original groups by the reducing division. 

 The great variability of hybrids of the second generation 

 proves that this only occurs very rarely, and in most instances 

 not at all. 



We have seen that the difference between reversions in 

 hybrids and in human beings of the same race is simply due to 

 every idant of one parent, in the case of hybrids, containing 

 specific characters, so that all the idants of the one parent are 

 similar, and all the homologous determinants may also be 

 considered homodynamous. When therefore an ontogeny is 

 directed by the ids of one of the parent species only, the type 

 of this species is produced. The type of a human being, on the 

 other hand, is constituted by ids of very many different kinds, 

 no two of which are exactly alike, for each of them contains 

 determinants of a somewhat different kind from the rest ; and, 

 speaking generally, the type is in all cases only the resultant 

 of all these different components. The same type, or combi- 

 nation of characters, can only appear for a second time if the 

 same components are again brought together. Except in the 

 doubling of the fertilised egg in the case of ' identical ' twins, 

 this can, however, never occur, for a new combination of ids and 

 idants which never existed before arises every time fertilisation 

 takes place. Hence cases of complete reversion as regards 

 individual characters to a previously existing form, can never 



