THE MECHANISM OF SEX-DETERMINATION 57 



In order to simplify the case let us imagine that each 

 sperm has only four chromosomes and the egg nucleus 

 only four. Let us represent these by the letters as 

 shown in Fig. 32. Any one of the four cells that is 



Fig. 32. — Diagram illustrating the irregular distribution of the chro- 

 mosomes in dispermic eggs in an imaginary case with only four kinds of 

 chromosomes, a, b, c, d. There are here three sets of each of these in 

 each egg. The stippled cells are those that fail to receive one of each 

 kind of chromosome. (After Boveri.) 



produced at the first division of these dispermic eggs 

 may contain a full complement of the chromosomes, 

 or only some of them. The possibilities for four 

 chromosomes are shown in the diagram. Any cell 

 that does not contain at least these four chromosomes 

 is shaded. One case is present in which all the four 



