112 Embryonic Development of Ovary and Testis of Mammals 



tinguished from the stroma nuclei nor from those of the peritoneum, 

 all of the above named being amoeboid in shape, and giving the appearance 

 of dividing by amitosis. 



A few large, well-marked, primitive sex cells are found in the rete 

 tubules, beneath the sex gland and in those lying well within the 

 anterior portion of the mesonephros in front of the sex gland. 



Testis. — In the anterior end of the testis the sex cords are still 

 attached to the peritoneum. They reach a considerable length, and 

 are often seen to branch once or twice in their course. More pos- 

 teriorly one finds cords in process of separation from the perito- 

 neum. As in the 1.7 cm. pig embryo, the nuclei of the proximal ends 

 of these separating sex cords are becoming elongated and are assum- 

 ing the character of connective tissue elements. Finally they break 

 away from the basement membrane to form the albuginea dividing the 

 peritoneum from the sex cords. More posteriorly still, this process 

 is found to have been completed. 



Ovary. — In the ovary, the sex cords have not begun to separate 

 from the peritoneum, although the introductory stages of such a pro- 

 cess are seen. The sex cords are not so definite in outline as are 

 'those of the testis, owing to the fact that the stroma tissue separating 

 them is not so dense as in that organ. The cells of the ovary are in 

 all regards quite like the corresponding ones in the testis, the same 

 small, amoeboid nuclei being found in the sex cords, rete tubules, 

 stroma and albuginea, in addition to the primitive sex cells of rete 

 tubules and sex cords. 



The peritoneum of the ovary is much thicker than that of the testis, 

 being three cells thick in many places. Primitive sex cells are found 

 occasionally in the innermost portions, together with intermediate 

 forms connecting them with the ordinary peritoneal cells. The inner 

 edge of the peritoneum is more or less irregular in outline, showing a 

 number of short, rounded protuberances — the rudiments of the cords 

 of Pfliiger. 



17-Day Embryo. Testis. — The seminiferous tubules of the testis 

 contain primitive sex cells and germinative cells, with many transi- 

 tional forms between the two. Both kinds divide by mitosis. The 

 stroma nuclei are now more regular in shape, and no longer give the ap- 

 pearance of dividing by amitosis. As in the pig embryo, an investing 

 membrane of connective tissue is found around the seminiferous tubules. 

 This tissue has undergone a decided 'increase. 



Cases of karyolytic degeneration are seen here and there among 

 the cells of the seminiferous tubules and rete tubules, although it is 

 by no means common. 



