THE STEUCTURE OF FREE-MARTIN GONADS 71 



diately under the compactly arranged fibers are similar fibers 

 more loosely arranged and enclosing blood-vessels. The position 

 and structure of this vascular zone makes it homologous with 

 the tunica vasculosa of the normal embryonic testis in cattle 

 (fig. 4). Its existence as a distinct layer in the normal foetal 

 testis is lost shortly before birth, through an increase in connec- 

 tive-tissue fibers and its intimate union with the tunica albu- 

 ginea (table 3 for details) . Thus the two layers are merged into 

 one thick layer, known as the tunica albuginea, the inner por- 

 tion of which contains the blood-vessels. It is thus seen in this 

 free-martin gonad that the embryonic relationships of the tunica 

 albuginea and tunica vasculosa are retained. 



Gonad H-40 (fig. 2) the oldest one of the entire series, is 

 undergoing certain pathological changes. Of chief importance 

 is the infiltration of connective-tissue fibers into the sex-cord 

 region, thereby crowding out some of the sexual cords and the 

 interstitial cells. The sex-cord region is approximately reduced 

 to a crescentic area which surrounds the rete region except where 

 the rete comes in contact with the tunica albuginea. The tunica 

 albuginea and the tunica vasculosa are not distinguishable 

 as they are in 11-36, but the blood-vessels are scattered through- 

 out the inner portion of the thickened capsule (fig. 2, bv). The 

 connective-tissue fibers of the tunica albuginea are very com- 

 pactly arranged, and this arrangement is maintained and con- 

 tinued on into the sex-cord region, so that no line of demarka- 

 tion can be recognized between the sex-cord region and the 

 tunica albuginea. Comparatively, the tunica albuginea of this 

 free-martin gonad has overgrown the usual limits of this struc- 

 ture in free-martin sex glands. 



The sex-cord region. Immediately under the tunica vasculosa 

 of H-36 a faint trace of a sex-cord region may be recognized. It 

 is represented by only a few sexual cords which in structure 

 resemble seminiferous tubules. Each tubule has a slightly 

 thickened connective-tissue wall, within which is a syncytium 

 of supporting epithelial cells (Sertoli cells). Germ cells are 

 entirely absent. 



