VARIATION 425 



uents are. however, not removed in this process ; on the con- 

 trary, the occurrence of ' pseudo-monogonic heredity' proves 

 that every parent-organism transmits the whole of them to the 

 offspring ; every pritiiary constituent is, hoauever, represented by 

 only half the tininber of determinants. 



From this theoretical basis, the results arrived at by breeders 

 are easy to understand. 'Like begets like,'' is their chief maxim, 

 and this is true whene\er two individuals are coupled which 

 possess a certain character as an inheritance transmitted 

 through a long series of generations. For such a character 

 must be represented by homodynamous determinants in the 

 great majority of ids in the germ-plasm ; and as it consequently 

 will not be entirely removed from either half of the latter by 

 the reducing division, it will in most cases be represented in a 

 majority of ids in the offspring. 



The idea that the 'increase^ of a 'character' can be produced 

 simply by crossing, is due to an inaccuracy of expression. ' Like 

 begets like,' but not something else ; and in this respect theorv 

 and practice agree. It is theoretically inconceivable that pre- 

 cisely the same part — that is to .say. the same determinate or 

 group of determinates — may be increased merely by the pairing 

 of parents possessing it. If, for instance, two individuals of 

 Lyccena agestis pair, and each of them possesses a white spot 

 instead of a black one, in the centre of the wing, none of the 

 offspring could exhibit a spot twice as large as, or even any 

 larger than, that of the parents. For the spot is controlled by 

 one or more homologous determinants, and if those of the white 

 variety are in the majority, the spot will be of this colour ; but 

 the adjacent determinants cannot thereby become modified. 

 The spot can at any rate only become pure white in case it was 

 previously merely grey, owing to the relatively larger number of 

 ' black ' determinants which took part in the control of the spot 

 in the parents having now been completely excluded from the 

 control of the cells by a preponderating majority of * white ' 

 determinants. 



The term 'quality' or 'character' (• Eigenschaft ') is the real 

 cause of confusion in this instance. In the Introduction to this 

 book I pointed out that this term may have several different 

 meanings with regard to heredity. Whiteness in plumage, for 

 example, is a *' quality ' which a breeder tries to obtain by alwavs 

 selecting the whitest bird for breeding purposes. From a breed 



