THE STRUCTURE OF FREE-MARTIN GONADS 81 



The sexual cords are of two types, those resembhng medullary 

 cords and those resembling seminiferous tubules. The former 

 resemble the medullary cords of the normal ovary in that they 

 are solid strands (cords) of irregularly arranged and closely 

 packed supporting epithelial cells forming a syncytium, which 

 may be regarded as the primordium of a Sertoli-cell syncytium. 

 In the free-martin, germ cells are absent from the medullary 

 cords. These sexual cords are not only structurally different, 

 but they are smaller than the sexual cords which resemble 

 seminiferous tubules. Cases 66 and 42 show distinct transi- 

 tional stages in the transformation of medullary cords into 

 seminiferous tubules through increase in size and rearrangement 

 of the nuclei of the syncytium. 



In such transitional stages, the nuclei are two and sometimes 

 three layers deep, and less crowded together than in the medul- 

 lary cords and accompanied by a slight increase in the size of 

 the cords. In the most completely transformed sexual cords 

 (seminiferous tubules), there is a further increase in size accom- 

 panied by the arrangement of the nuclei of the supporting 

 epithelium into a single layer at the periphery. The oval nuclei 

 of this layer are arranged with their long axes perpendicular to 

 the wall of the tube. Extending from the inner ends of the 

 nuclei are strands of cytoplasm, all of which meet at the center 

 of the seminiferous tubule (fig. 6, s). Such a center has a 

 potentiality of forming a lumen, as in the normal seminiferous 

 tubule (figs. 7 and 8). If this syncytium of supporting epithelial 

 cells is compared with that of the mature foetal testis (fig. 7) 

 and a young calf testis (fig. 8), a close structural similarity will 

 be seen, with one important deficiency, namely, that germ 

 cells of any stage are absent from the syncytium of the free- 

 martin seminiferous tubule. It may also be noted that in the 

 tubules of the free-martin there is much less regularity in the 

 arrangement of the nuclei of the supporting epithelial cells; in 

 this respect the arrangement is like that of very young foetal 

 testes (table 3). 



Each wall of these sexual cords is composed of a basement mem- 

 brane upon which the supporting epithelial cells rest, and external 



