LIMITS OF HEREDITARY CONTROL 911 
anced chromosomal relations of the female and variational stability 
on the one hand, and between the unbalanced condition of the 
chromosomes in the male and its variational instability on the 
other? If such a connection exist we have, in addition to sex, 
another character whose physical basis may in some way be asso- 
ciated with the dimorphism in the chromatin content of the fer- 
tilized egg. 
A further suggestion might be made in this connection. It 
seems to be an established fact that the male sex is the more highly 
specialized, for males depart more widely from the juvenile type 
than do females. Might it not be possible that the unstable equi- 
librium of the male chromatin complex lies at the basis of the higher 
specialization of the male; for a condition of instability would 
involve an increased potentiality for progressive change? Is 
there any more or less justification for these suggestions than 
there is for the generally accepted idea that sex is in some way 
causally associated with the presence or absence of the accessory 
chromosome, or its equivalent? 
GENERAL CONSIDERATIONS 
In his chapter on blastogenic variation Vernon quotes from 
Weismann the statement that ‘‘the individual is determined at 
the time of fertilization, or, in other words, the individuality of the 
organism results from the fact that the germ-plasm is composed 
of the paternal and maternal ids which are brought together in 
the egg cell.” As evidence of the validity of this statement the 
author brings up the facts about human identical twins and on 
the basis of these facts claims that ‘‘ heredity is potentially decided 
at the time of fertilization.” 
In the present paper we have shown that the individuality of 
the organism is not precisely determined at the time of fertiliza- 
tion, but that the characters are hereditarily controlled only within 
certain limits. These limits we have been able to define with 
respect to a number of different characters. 
Our results are based on the assumption that the degree of 
divergence shown between the four foetuses is the index of the 
