44 



CHORD AT A. 



The thickened germinal epithelium gives rise (in the case of the 

 female) to the ova and the follicular epithelium. Whether the 

 genital ridge is provided with a core of stroma or no, the germinal 

 epithelium is always in contact on one side with the stroma, from 

 which it is at first separated by a well-marked boundary line ; but 

 after a certain time there appear numerous vascular ingrowths from 

 the stroma, which penetrate through all parts of the germinal 

 epithelium, and break it up into a sponge-like structure formed of 

 trabeculae of germinal epithelium interpenetrated by vascular strands 

 of stroma. The trabeculse of the germinal epithelium form the egg 

 tubes of Pfliiger. 



With reference to the distribution of the stroma in the germinal 

 epithelium, it may be said in a general way that there is a special 

 layer close to the surface of the ovary, which, after the formation of 

 fresh ova has nearly ceased, completely isolates a superficial layer of 

 the germinal epithelium from the deeper and major part of it. The 

 superficial layer is frequently (but erroneously) regarded as consti- 

 tuting the whole of the germinal epithelium. The layer of stroma 

 below the superficial epithelium forms in the mammalian ovary the 

 tunica albuginea. As the follicles are formed in the trabeculae of 

 germinal epithelium the stroma grows in around them, and forms 

 for each one of them a special tunic. 



FIG. 18. TRANSVERSE SECTION THROUGH THE OVARY OP A YOUNG EMBRYO OF SCYLLIUM 

 CANICULA, TO SHEW THE PRIMITIVE GERMINAL CELLS (po) LYING IN THE GERMINAL 

 EPITHELIUM ON THE OUTER SIDE OF THE OVARIAN RIDGE. 



The adult ovaries differ in a corresponding manner to the em- 

 bryonic genital ridges as to the presence of a core of stroma. The 

 ovaries which are without such a core in the embryo, are ako 

 without it in the adult, and are formed of a double layer of tissue 

 entirely derived from the germinal epithelium with its ingrowths of 

 stroma, and composed, for the most part, of ova in all stages of 

 development. In the case of the other ovaries there is a hilus of 

 stroma the zona vasculosa internal to the egg-bearing region. 



