408 EMBRYOLOGY. 



epithelium from the adjacent part of the primitive kidney 

 (in Reptiles and Birds from the epithelium of Malpighian 

 glomeruli). 



21. The specific components of the sexual glands, the eggs and 

 seminal cells, arise from the germinal epithelium (with its primitive 

 ova and primitive seminal cells). 



22. In the female there arise, in consequence of a process of 

 mutual intergrowth on the part of the germinal epithelium and the 

 subjacent stroma, the tubes of Pflugee and egg-balls (or nests), and 

 out of these finally egg-follicles, containing each a single ovum ; in 

 the male there are formed, in consequence of a similar process, seminal 

 ampullfE (Selachians, some Amphibia) or seminal tubules (tubuH 

 seminiferi) with their seminal mother-cells. 



23. The sexual cords of the primitive kidney participate in the 

 composition of the medullary substance of the ovary as medullary 

 cords ; in the testis they unite with the seminal ampuUse or seminal 

 tubules and furnish the tubuU recti and the rete testis, consequently 

 the initial part of the outlet for the semen. 



24. The ovarian follicles are composed of a centrally located ovum, 

 an envelope of follicular cells, and a vascular connective-tissue capsule 

 (theca foUiculi). 



25. In Mammals the ovarian follicle is converted into a Graafian 

 follicle by an increase in the number of follicular cells and by their 

 secreting between them a follicular fluid. (Discus proligerus, mem- 

 brana granulosa.) 



26. The Graafian follicles, after the elimination of the mature ova 

 into the abdominal cavity, become the so-called yellow bodies in the 

 following manner : blood flows out of the ruptured blood-vessels 

 into their cavities, and both the follicular cells left behind and the 

 connective-tissue capsule undergo proliferation accompanied by an 

 emigration of white blood-corpuscles (true and false corpora lutea). 



27. The yellow bodies subsequently cause by their scar-like shrivel- 

 ling the cicatriculiB and callosities on the surface of old ovaries. 



28. The canals and glands of the urogenital system, which are at 

 first established in the same form in both sexes, are afterwards 

 difierently employed in the male and female and undergo a partial 

 degeneration. 



29. In the male the mesonephric duct becomes the vas deferens, 

 in the female it becomes rudimentary (Gaetner's duct, in many 

 Mammals). 



30. The Miillerian duct assumes in the male no function, and 



