Distribution of the Primary Hereditary Characters 173 



binations are formed in the half-groups derived from dif- 

 ferent nuclei, even of the same parent. 



This diversity of the combinations of the primary hered- 

 itary characters in the different half nuclei is the essential 

 point in understanding the way the later hereditary char- 

 acters are distributed, so that it will be best to illustrate 

 how it comes about. Suppose we represent the chromosomal 

 packages in the nuclei of a particular animal by letters of 

 the alphabet. We will indicate the diversities by giving 

 a different letter to each chromosomal packet, and to the 

 two members of a given pair we will give a capital letter 

 and a small letter respectively. To illustrate the principles 

 in simple form, we will suppose that there are but four pairs 

 of chromosomal packages in each nucleus. That is, the 

 chromosomes of each nucleus would be represented as fol- 

 lows: 



A B C D 



abed 



Now in each parental nucleus of this kind the chromosomes 

 separate into two groups, one member of each pair in each 

 group. But either member of any pair can go into either 

 group. That is, from one nucleus the two groups formed 

 may be A B C D and abed; from another nucleus they 

 are A B c D and a b C d ; from another A b C d and a B c D, 

 and so on. The number of different combinations from 

 four pairs is 16, and each occurs as frequently as any other. 1 



So from a number of parental nuclei, all having the same 

 combination of packages, a large number of different com- 

 binations will be formed in the half nuclei. 2 



1 These facts, fundamental for the understanding of the rules of in- 

 heritance, have recently been directly demonstrated for certain higher 

 organisms, by Carothers (1917). 



" The number of diverse combinations possible in the half nuclei 

 formed from nuclei all of the same kind is 2 n f if n is the number of 

 diverse pairs of chromosomes present in the original nuclei. 



