Sex as an Adaptation 429 
Both Flourens and Cuénot found this to be the case in the 
few instances that they examined, but Cuénot has shown that 
this does not always happen. Even when this occurs, it has 
not been determined whether the result depends on something 
in the egg itself, that causes a male egg to be set free first, or 
on some external condition that determines that the first egg 
shall become a male. It has been claimed that the age of 
the spermatozoon might in this and in other cases determine 
the result; but Gerbe has shown that if the domestic hen is 
isolated for fifteen days after union with the male, she will 
continue to produce fertile eggs from which both sexes are 
produced, without showing any relation between the time 
the eggs are laid and the particular sex that develops. 
Cuénot does not discuss whether sex is determined by the 
nucleus or by the protoplasm, but if, as he thinks probable, 
the size of the egg is a determining factor, it would appear 
that the protoplasm must be the chief agent. Even if this 
were the case it would still be possible that the size of the 
egg itself might be connected with some action on the part 
of the nucleus. If, as seems probable, identical twins come 
from halves of the same egg, then, since they are of the same 
sex, the absolute amount of protoplasm cannot be a factor 
in sex determination. 
As a basis for the discussion that follows, certain processes 
that take place during the maturation divisions of the egg 
and of the spermatozoon must be briefly noticed.: After the 
egg leaves the ovary it extrudes a minute body called the 
first polar body (Fig. 6 B, C, D). This process of extrusion 
is really a cell division accompanied by the regular mitotic 
division of the nucleus; but since one of the products of the 
division, the polar body, is extremely small, the meaning of 
the process was not at first understood. The half of the 
nucleus, that remains in the egg, divides again, and one of its 
halves is thrown out into a second polar body (Fig. 6 E, 
F, G). Meanwhile, the first polar body has divided into two 
