ZOOLOGY: F. R. LILLIE 
469 
except D. Berry Hart's statement concerning the gonads of Hunter 
free-martins, that ^'in only one are spermatozoa present." More than 
six words seem necessary to establish so important an exception. 
Regarding other parts of the internal reproductive system we have 
seen that the free-martins exhibit a graded series of inhibition of the 
female ducts and of development of the male ducts which may obviously 
correspond to variable time of onset, intensity, and perhaps duration 
of action, on the male sex-hormones. The series extends nearly to the 
normal male limit in exceptional cases. There is indicated a rough 
paralleKsm at least between the grade of transformation of the gonad 
and that of the remainder of the internal reproductive system. The 
external organs of reproduction are the least liable to modification, 
but they do not escape in all cases, and may even exhibit considerable 
transformation in the male direction, if we can accept Numan's case. 
The fundamental determining factor in these events is undoubtedly 
the male sex-hormones as has been argued previously, but the entire 
causal nexus is by no means clear. We do not know what the results 
of embryonic castration of the female might be in itself, and hence we are 
unable to assert definitely in just what positive ways the male hormones 
act on the female zygote, because the earliest determinable result of 
such action is the suppression of the ovarian cortex, which must be re- 
garded as practically equivalent to castration. This action at least is 
due to the male hormones ; how much of the subsequent events is due to 
mere absence of ovarian tissue, and how much to positive action of male 
sex-hormones is more or less problematical. It is well known that spayed 
females of certain birds and mammals tend to develop male characters; 
heifers with cystic degeneration of the ovary also develop certain male 
characteristics (Pearl and Surface, 1915),'° so that we must admit in 
principle the possibihty that much of the male development in the free- 
martin is due to the lack of inhibitions normally furnished by the ovary. 
It is also probable that the various parts of the reproductive system 
have other means of correlation, and act and react on one another in 
various ways. Certain indications of this are seen in lateral variations, 
as for instance in one of my cases where a large gonad on one side is 
associated with a large Wolffian duct, and seminal vesicle, and a much 
smaller one on the other side with a correspondingly smaller duct and 
vesicle. 
When, therefore, we attribute the free-martin condition to the male 
hormones we only mean to assert that they are the primary cause, and 
not that they are the decisive factors in each member of the series of 
events. 
