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, 
