Embryology. 525 



interstices occupied by very minute granules, which are the starting 

 point for the formation of the yolk spherules. 



These yolk spherules form first near the nucleus and then towards 

 he periphery of the egg. In this way is formed what appears to be 

 yolk at the center of the ripe egg. 



of yolk is made gradually by the conversion of 

 ayers of granules into yolk spherules. These layers are 

 brmed outside the central mass and close to the tunica adventitia, the 

 being the outermost. Some of these layers become con- 

 verted into yellow yolk. 



The peripheral granular layer of the egg grows and is nourished by 

 he aid of the zona radiata. This peculiar layer is formed, now, 

 »etween the tunica adventitia and the granular outermost part of the 

 egg and remains as long as yolk formation continues. Though appar- 

 ently a part of the ovum, this layer is, the author holds, in reality a 

 system of parallel radiating fibrils which are merely processes of the 

 bllicle cells ! These processes pass through holes in the tunica adven- 

 itia and at the other end become continuous with the mesh-work of 

 ;he peripheral part of the ovum. 



The follicle (stroma) cells and the ovum are thus united by inter- 

 cellular processes, by which nutrient liquids may pass into the ovum. 

 When the egg finally escapes from the ovary some fibrillar rem- 

 nants of this zona radiata remain adherent to the inner side of the 

 tunica adventitia and thus cause the somewhat double nature of the 

 " vitelline " membrane. 



No observations were made upon the proper maturation of the 

 ovum, though certain peculiar bodies in the nucleus are regarded as 

 preparations for the formation of the polar cells. 



Sexual Glands in Mammals and in the Fowl. 1 — Dr. J. 

 Janosik, from sections of embryos of the fowl, the sheep, the hog and 

 man, has arrived at the following interesting conception of the nature 

 of the genital glands, in reference to sex. 



A proliferation of cells of the germinal epithelium gives rise to 

 strings of cells which are to be later developed in the male (testis) but 

 which in the female (ovary) are not developed. A second prolifera- 

 tion of the epithelium gives rise to the nests of cells to form the ova of 



The gland, ovary or testis, thus has a central, older, part that may 

 become the male portion, and a peripheral, younger part that may 

 •Janosik: Sitzb. Akad. Wiss. Wien, 1890, pp. 260-2SS, pi. I. 



