THE GENESIS OF LIVING ORGANISMS 201 



Only in exceptional cases are the recessive rudiments incom- 

 pletely suppressed, and so produce a modification of the 

 dominants. Thus the offspring of the black race of 

 Andalusian fowls crossed with white are not black, but 

 blue. Such modified properties can sustain competition 

 with the rudiments in the full-grown organism ; but, as we 

 shall see presently, they furnish no constant racial characters. 

 They appear only when the recessive property shines through 

 the dominant. 



In the majority of cases, the dominance is absolute, and 

 crowds out the recessive property altogether. This exclusion, 

 however, refers only to the organism immediately proceeding 

 from the germ. Part of the germ remains unaltered, and 

 gives the sexual cells from which the next generation springs. 

 This part of the germ, whether it gives rise to male or to female 

 products, contains at first both recessive and dominant rudi- 

 ments unaltered side by side. At maturation of the germ- 

 cells, there ensues, according to Mendel, a separation of the 

 competing rudiments, so that, before crossing, both male 

 and female germ-cells contain only one rudiment for each 

 character of the body. 



For this reason, the properties emerging modified from 

 the competition (like the blue of the Andalusian fowl) are not 

 further inherited as independent properties, but always appear 

 only when a fresh crossing unites the rival rudiments. 



It follows from Mendel's demonstrations that all offspring 

 of the first generation, which comes from different races, 

 possess germ-cells, half of which show paternal, and the other 

 half maternal rudiments. If these sex-cells are crossed 

 haphazard, then, according to the rule of probability, one- 

 fourth of the zygotes must contain only paternal, one-fourth 

 only maternal rudiments, while half contains the competing 

 rudiments from the two parents. 



