58 THE CONTROL OF LIFE 



is the same in quite unrelated organisms, e.g. white 

 man and slug ; the point is the constancy of the number. 



(6) The paternal and maternal contributions form 

 the warp and woof of the web which composes the 

 organism, and each sex-cell carries a complete set of 

 the essential hereditary qualities. In the course of 

 development, however, the offspring may 'take after*, 

 one side of the house as regards one character, and 

 may * favour ' the other side of the house as regards some 

 other character. It may be like the father in its hands, 

 like its mother in its hair. Thus we have to distinguish 

 between the inheritance or ' genetic composition ' which 

 the organism has to start with, and the expression 

 of that inheritance in development. 



(7) Strictly speaking, an inheritance is multiple as 

 well as dual, for there may be demonstrable ancestral 

 contributions which did not find expression in the 

 parent. Resemblance to a grandparent is a common 

 and, as we shall see, readily explicable phenomenon. 

 Characters sometimes lie latent for a generation, or 

 for several generations, which again brings out the 

 difference between the implicit inheritance and the 

 developmental expression of it. 



(8) The largest fact of heredity is that like tends to 

 beget like. The hereditary relation between successive 

 generations is such that a general resemblance is sus- 

 tained. A particular kind of organisation, associated 

 with a particular kind of activity, persists from genera- 

 tion to generation. These are simply different ways of 

 saying the same thing ; that all inborn characters 



