THE OVUM. 55 



like structure formed of trabeculae of germinal epithelium inter- 

 penetrated by vascular strands of stroma. The trabeculae of the 

 germinal epithelium form the egg-tubes of Pfliiger. 



With reference to the distribution of the stroma in the germi- 

 nal 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 errone- 

 ously) regarded as constituting the whole of the germinal epi- 

 thelium. 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. 1 8. TRANSVERSE SECTION THROUGH THE OVARY OF 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 

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

 tissue entirely derived from the germinal epithelium with its in- 

 growths of stroma, and composed, for the most part, of ova in 

 all stages of development. In the case of the other ovaries there 



