114 Embryonic Development of Ovary and Testis of Mammals 



23-Day Embryo. Testis. — In the testis of this stage there is no 

 important advance over the preceding stage. 



Ovary. — The rete tubules have assumed the appearance of the 

 medullary cords save for the fact that they contain no primitive sex 

 cells — a fact which might have been noted in the 21-day embryo. 

 There has been little essential change in their general character. The 

 nuclei of the rete tubules and their homologues in the medullary cords 

 are still very irregular in form, giving the appearance of being in pro- 

 cess of division by amitosis. Undoubted amitosis occurs among simi- 

 lar nuclei in the cords of Pfliiger (Plate VI, Fig. 22). These are des- 

 tined to become the follicular (granulosa) cells of the Graafian folli- 

 cles. It is possible that some of them may develop into oogonia — 

 this point should be studied further. The cords of Pfiliger are con- 

 nected with the peritoneum by slender necks. 



26-Day Emhryo. Testis. — The rete tissue has extended the en- 

 tire length of the testis. Scattered primitive sex cells are found here 

 and there in the part lying within the testis, but are not present in 

 the mesonephric portion. 



The interstitial cells are found to occasionally divide by mitosis. 



There is an extensive karyolitic degeneration of sex cells of the 

 seminiferous tubules. Not only is the nucleus affected in the man- 

 ner already described, but the cytoplasm undergoes modification a,s 

 well, in that it assumes the property of staining more deeply in these 

 degenerating cells than it does in the normal ones. 



Ovary. — The medullary cords are now clearly separated from one 

 another by rather wide intervals filled with stroma tissue. The cords 

 of Pfiiiger have increased in extent and have, to a large extent, fused 

 with one another until their original limits are marked only by dense 

 plates and strands of connective tissue. As in the pig, we shall here- 

 after refer to this zone of densely-packed cords of Pfliiger as the cor- 

 tex, in contradistinction to the inner core of looser tissue made up of 

 stroma and medullary cords. 



Rabbit at Birth. Testis. — The rete tubules become more distinctly 

 limited from one another and have begun the process of lumen forma- 

 tion simultaneously in all parts of the rete tissue. In this process 

 the cells pull apart from the central axis of the cord which is a line of 

 weakness due to the manner in which these cords are formed. The 

 lumen of any given rete tubule is not continuous at first, being formed 

 disconnectedly along the course of the cord. Each tubule is provided 

 with a connective tissue sheath. Tlie typical epithelial cells of these 

 tubules form a syncytium in which the deeply-staining, columnar 



