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ZOOLOGY: C. E. McCLUNG 
well marked differences both in time and degree of its action. If the results 
of the activities of the cell are due to the ordered interaction of its parts, then 
any change in the rate of any one of its controlling elements, or any modification 
of its time of action, must essentially affect the product. The sex-chromosome 
during the development of the male germ cells exhibits all the signs of such a 
differential action. In the first stages it is much more active than the other 
chromosomes, as is evidenced by the large surface it exposes at the time of 
greatest cellular interaction. Not only is this true but it is more independent, 
having its substance isolated in a separate region. From this behavior it 
is clear why it should, in the single condition here, be quite as effective in its 
action as the duplex element of the female, if similar activities prevail in the 
body cells. 
At a later stage, when it is almost certain that the new relations between 
controls of characters are being established, the sex chromosome is withdrawn 
and has its surface reduced to the least possible extent. It gives every evidence 
of inactivity, and, indeed, at this time has no occasion for action, since it has 
no homologue with which to react. In cases, unlike the Orthoptera, where 
there is a member to pair with it, the behavior is much the same and the genetic 
evidence would indicate the absence of any reaction. 
Undoubtedly this is indicative of the real difference between the female and 
male organization, and, when fully understood, will point to the meaning of 
sex. It is possible that we have here the explanation of the greater variability 
of the male, for if a part of the control system is thus withdrawn from action 
at the time of reorganization it would, almost inevitably, affect the entire 
result. Here it may be recalled that there has been much dispute regarding 
the general significance of sexual reproduction, some holding that it is to 
ensure variation, others that it is to control or prevent it. Since both of these 
ends must, in some measure, be attained is it not entirely possible that the 
sexes represent, in part, such a division of labor? In this connection it may 
be pointed out that the history of the sex chromosome is such as to fit it 
exactly for the role of furthering these two purposes. It passes alternately 
from the male to the female line, in the one being subject to the relative in- 
stability of its unpaired condition, in the other being an orderly member of a 
balanced series, forced to react with its mate as do the other chromosomes. 
There is a possibility that in the male, the sex chromosome being unmated, or 
opposed by an inactive element, may be more free to react with the other 
chromosomes and in this way change their constitution, being in turn affected 
by the reaction. By the nature of its transmission it must, after this experi- 
ence, pass into the female line where its relation to the complex is necessarily 
different. The contrast in these two conditions is obvious and the interpreta- 
tion strongly suggested. 
Where there is a mate to the sex chromosome in the male the genetic results 
would indicate that it has no function, and the very fact that it may indiffer- 
ently be present or absent suggests its inactivity. This element, of all the 
