DIMORPHISM AND POLYMORPHISM 353 



and the parental forms, none of the characters of one of the 

 parents are present in a latent condition. 



Such a rapid removal of characters from the germ of indi- 

 vidual descendants is, however, only possible if — as in the case 

 of these hybrids — they belong to one parent only. Thus in 

 the human race, any individual traits of the mother or father 

 may not only be absent in certain of the children, but the 

 corresponding determinants may even be wanting in their 

 germ-plasm, so that these traits cannot reappear in the grand- 

 children or great-grandchildren. The case, however, is very 

 different with regard to those characters which are possessed 

 by both parents. These cannot disappear from the germ- 

 plasm of individual descendants from one generation to the 

 next, for their determinants constitute a majority in the maternal 

 as well as in the paternal half of the germ-plasm. As long as 

 these characters are present in all the individuals of the group 

 of forms in question, the determinants for these characters will 

 predominate in most of the idants, and it will then hardly be 

 possible for them to dwindle into a minority in consequence of 

 successive reducing divisions. But let us take the case of a 

 gradually disappearing character, and select as an example the 

 wing-bars characteristic of the rock-pigeon which are present in 

 the domesticated breeds. The absolute number of the 'wins- 

 bar' determinants in the germ-plasm must have been diminished 

 gradually in the course of the processes of selection which led 

 to the formation of the various races, owing to many of them 

 becoming transformed into differently constituted or 'modern' 

 determinants. The smaller the number of 'ancestral' deter- 

 minants, the more liable are they to be totally eliminated from 

 one half of the germ-plasm in the reducing division. When, 

 however, they are entirely wanting in individual germ-cells, tw'o 

 of these cells may possibly come together in conjugation ; and 

 an animal would then be produced which possessed no 'wing- 

 bar ' determinants, or, in other words, which no longer contained 

 this character in a latent condition. In proportion as such 

 individuals became more frequent, the average number of ' bar ' 

 determinants in the germ-plasm of the race must still further 

 decrease, owing to the constant interbreeding of these indi- 

 viduals with others, until finally only a small percentage of 

 individuals would contain such determinants at all. 



I do not think that the above argimient can be strictly applied 



