THEORIES OF HEREDITY 67 



if we assume them represented diagrammatically in a 

 circle, the division does not necessarily separate each time 

 2 Idants with identical Ids, but may fall near the point 

 of junction of the Idants, and divide the Idants in such 

 wise that the new Idants A^, B^, C^, and D^, each have 

 5 Ids of one kind and i of another kind — i.e., A^ =5^+ ic, 

 W =^b-\-ia, O- ='^c + id, and T)^=^d+ih. If the same 

 now happens to the new Idants of the next generation, and 

 so on during many generations, we shall finally get Idants 

 containing Ids all of a different character. As each Id 

 represents a complete individual, we have therefore in the 

 germ-plasm represented many individuals of different 

 tendencies and characters. 



Furthermore, the reducing division, by removing each 

 time one set of chromosomes from the germ-cells, leaves 

 them with a variety of different chromosomes, so that we 

 get from each individual a variety of germ-cells, each ex- 

 pressing different hereditary tendencies and characters. 

 Thus, let us assume we have a germ with four chromo- 

 somes, ABCD. As each time during the reducing 

 division a set of two chromosomes is removed, we have the 

 possibility of six different germ-cells, containing two 

 chromosomes each — viz. : 



AB, BC, CD. 



AC, BD. 

 AD. 



Each of these, of course, expresses different hereditary 

 traits. But we further know that before the reducing 

 division a doubling of the chromosomes takes place. This, 

 according to Weismann, has the purpose of still further 

 increasing the' variety of germ-ceUs. 



If we take again a germ with four chromosomes, ABCD, 

 and we double these, we get 



ABCD 

 ABCD. 



