134 THE BREEDING OF ANIMALS 



relation between parents and offspring. This relation is 

 a universal biological phenomenon and is called heredity. 

 There exists a continuous line of descent from generation 

 to generation. The mechanism of heredity is to be found 

 in the protoplasm of the germ-cells. The stream of 

 descent is from germ-cell to germ-cell. The soma- or 

 body-cells constitute in a sense only a temporary abiding 

 place for the germ-plasm. 



125. Heredity and variation not antagonistic. It is 

 not stating the facts correctly to maintain that the tend- 

 ency of offspring to be like the parent, which we call 

 heredity, is opposed by the universal tendency of organ- 

 isms to vary. These are but two phases of the same 

 phenomenon. "Living beings do not exhibit unity 

 and diversity," says Brooks, " but unity in diversity. 

 These are not two facts but one. The fact is the indi- 

 viduality in kinship of living beings. Inheritance and 

 variation are not two things but two imperfect views 

 of a single process." There is a sense, of course, in which 

 variation is opposed to heredity. It is conceivable that 

 recombinations of characters may occur in the germinal 

 substance, and these new combinations may cause such 

 modification of characters already present that the new 

 organism may be radically changed. 



Heredity is the genetic relation of parents and offspring. 

 On the average the offspring will be like the parents. 

 But this relation admits of variations within more or less 

 definitely prescribed limits. The offspring have an 

 individuality all their own, but this does not preclude the 

 existence of a genetic continuity which is the common 

 heritage of parents and offspring. 



126. The kinds of heredity. Every individual is 

 the result of a union of the germ-plasm of two individuals. 



