418 FRANK R. LILLIE 



event a very difficult problem, and it seems worth while to in- 

 dicate the hitherto unconsidered possibility of action of hetero- 

 logic sex hormones, however brought about, in this connection. 



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, of the male sex- 

 hormones. The series extends nearly to the normal male limit 

 in exceptional cases (no. 44, fig. 28). There is indicated a 

 rough parallelism at least between the grade of transformation 

 of the gonad and that of the remainder of the internal repro- 

 ductive 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 described on p. 413 

 and illustrated in figure 29. 



The fundamental determining factor in these events is un- 

 doubtedly the male sex hormones as has been argued previously 

 (p. 396) ; 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 regarded 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 mam- 

 mals tend to develop male characters; heifers with cystic degen- 

 eration of ovary also develop certain male characteristics (Pearl 

 and Surface, '15), so that we must admit in principle the possibil- 

 ity 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 



