Sex as an Adaptation 427 
one that is more constructive is a female. Furthermore, 
whichever process is in the excess during development deter- 
mines the sex of the individual. Thus, if conditions are very 
favorable, there will be more females produced ; but if, on the 
other hand, there is an excess of the breaking-down process, 
males are produced. So far, the process is conceived as a 
purely physiological one, but to this the authors then apply 
the selection hypothesis, which, they suppose, acts as a sort 
of break or regulation of the physiological processes, or in 
other words as a directive agent. They state: “Yet the 
sexual dimorphism, in the main, and in detail, has an adaptive 
significance, also securing the advantages of cross-fertiliza- 
tion and the like, and is, therefore, to some extent the result 
of the continual action of natural selection, though this may, 
of course, check variation in one form as well as favor it in 
another.” Disregarding this last addition, with which Geddes 
and Thompson think it necessary to burden their theory, let 
us return to the physiological side of the hypothesis. Their 
idea appears to me a sort of symbolism rather than a 
scientific attempt to explain sex. If their view had a real 
value, it ought to be possible to determine the sex of the 
developing organism with precision by regulating the condi- 
tions of its growth, and yet we cannot do this, nor do the 
authors make any claim of being able to do so. The hy- 
pothesis lacks the only support that can give it scientific 
standing, the proof of experiment. 
There have been made, from time to time, a number of 
attempts to show that the sex of the embryo is predeter- 
mined in the egg, and is not determined later by external 
circumstances. In recent years this view has come more to 
the front, despite the apparent experimental evidence which 
seemed in one or two cases to point to the opposite view. 
One of the most complete analyses of the question is that 
.of Cuénot, who has attempted to show that the sex of the 
embryo is determined in the egg, before or at the time of 
