F. A. E. Crew 177 



logies of the gonads of the frco-martin shows that in th(; free-martin (a 

 sterile female co-twin to a normal male in cattle) an indifferent gonad 

 with a primary female determination, imder the influence of sex 

 hormones from the male twin, may develop variable degrees of trans- 

 formation in the male direction. So far as the structural evidence from 

 sixteen cases (seven foetal and nine postnatal) goes, the reproductive 

 glands of free-martins may be placed into three distinct groups, which 

 may be characterized as low, medium and high degrees of transformation 

 in the male direction, and constitute, therefore, a chain of connected 

 links between an embryonic ovary and a testis. Every organ of these 

 modified free-martin gonads is affected. The sexual chords exhibit a 

 series of gradations between medullaiy cords and seminiferous tubules 

 (complete except that male sex cells are lacking). The rete ovarii trans- 

 forms into a rete testis chiefly by developing connections {tiihnli recti) 

 between the rete tubules and the epididymal tubules. In the least trans- 

 formed gonads the epididymis is absent ; in gonads exhibiting a moderate 

 degree of transformation the head of the epididymis alone is present, and 

 in the most completely transformed gonads a complete epididymis is 

 developed. The distribution of the blood-vessels ranges from a typical 

 ovarian to a typical male arrangement. It is thus seen that the most 

 fundamental sex organ may be rather completely inverted by means of 

 hormones of the opposite sex. Sex differentiation, then, is not ex- 

 clusively determined by the union of the gametes. 



But, as is illustrated in the cases of abnormality already describerl, 

 the spermatic tissues may not become expressed until the ovarian have 

 attained functional maturity and it has been shown that the appearance 

 of a small amount of spermatic tissue upon the inner border of a gonad 

 which previousl}' has had every character of a normal ovary, is associated 

 with the immediate degeneration of the ovarian tissues and a gradual 

 but inevitable assumption on the part of the individual of the male 

 organisation. 



In these circumstances, if the gonal tissues exert their influence by 

 means of internal secretions, then that of the testis must be more 

 powerful by far than that of the ovary for the former wipes out the 

 ovarian tissues and directs the imposition of male characters. 



There is, in the frog, an antagonism of sex hormones and the ovarian 

 is powerless in the presence of the spermatic. Quantity, apparently, is 

 not a factor, for a very small nodule of testicular substance can still 

 provide sufficient of the male hormone to wipe out the g:-eat mass of 

 ovarian tissue and its abundant internal secretion. 



