SEX INHERITANCE 103 



somes (XxXx). Since the history of the sex chro- 

 mosomes alone furnishes certain information that 

 makes clear some of the changes in the life cycle, 

 the other chromosomes may be disregarded for the 

 present. 



Starting at the bottom of the diagram it will be 

 seen that the sexual egg after extruding the two 

 polar bodies contains two sex chromosomes indicated 

 by X and x. Two kinds of males are indicated in 

 the diagram, one containing Xx the other Xx', and 

 as a consequence there will be two kinds of female- 

 producing sperm, one kind for each male, namely, 

 Xx and Xx'. If the former fertilizes the sexual egg, 

 the resulting stem-mother will be XxXx, if the 

 latter, the stem-mother will be XxXx'. These two 

 kinds of stem-mothers are indicated at the top of 

 the diagram. One of them, XxXx, produces eggs 

 which, after extruding one polar body, give rise to 

 the migrants bearing large eggs; from the latter 

 eggs, in turn, come the sexual females. The other 

 stem-mother XxXx', produces eggs, which, after 

 extruding one polar body, give rise to the migrants 

 bearing small eggs. Prior to the time when these 

 small eggs are about to give off their single polar 

 body, the two large X's conjugate and the two 

 small x's conjugate, and when the polar body is 

 given off one large and one small X pass out, and 

 one large and one small X remain in the egg. In 

 other words there is at this time a reduction in the 

 number of sex chromosomes, and, as a consequence, 

 a male is produced. Now, as the diagram shows. 



