STUDIES IN THE EXPEEIMENTAL ANALYSIS OP SEX. 599 
But this caunot possibly apply to the infected males, because 
they develop the same female secondary sexual characters 
before there is any ovary present at all, much less a mature 
ovary ready to produce ripe eggs. Now these males, 
although they develop the female secondary sexual characters 
when there is no ovary present, yet subsequently they may 
regenei’ate an ovary from the shreds of germinal epithelium 
remaining from the degenerated testis. In other words 
they have the potentiality to produce an ovary, and we may 
safely argue that it is this potentiality which enables them 
to produce the secondary sexual characters befoi’e the actual 
ovary is there. 
In this conception it appears to me lies the solution of the 
uncertain nature of the correlation existing between primai’y 
and secondary sexual characters in general. It is not 
necessarily the pi-esence of a differentiated gonad producing 
some internal secretion which causes the development of the 
corresponding secondary sexual characters, but it is the 
potentiality to form that gonad. Thus the development of 
the secondary sexual characters is not primarily dependent on 
the gonad, but the development of both is dependent on a 
third factor. If we attempt to formulate what this factor 
actually is, it appears to me legitimate to represent it as the 
presence of a substance having the nature of an internal 
secretion, which circulates thi’ough the body and controls 
the differentiation of the primary and secondary sexual 
characters. I have called this hypothetical substance the 
“sexual formative substance,” and we must suppose that two 
kinds of it exist, male and female. By this theory we can 
account for the imperfect nature of the correlation between 
primary and secondary sexual characters, and also for the 
development of the female secondary sexual characters in 
infected male crabs before the development of an ovary, 
which is unaccountable on the theory that the ovary produces 
the substance necessary for the development of the secondary 
character. s. 
It is, however, a notorious fact that the mere removal of 
