106 Embryonic Development of Ovary and Testis of Mammals 



8.5 to 10 cm. Emhrijo. — Up to the stage when the embryo is 8.5 cm. in 

 length, the rete cords extend but a short distance straight in from the 

 hiliim in the case of both ovary and testis, and are similar in both 

 sexes, the primitive sex cells of the rete ovarii becoming larger than 

 those of the rete testis. 



The embryo of 10 cm. length shows the rete testis to have rapidly 

 developed an axial core of loose connective tissue that fills in the space 

 central to the free tips of the radially directed seminiferous tubules. 

 In the female, on the other hand, the rete ovarii extends no further 

 into the ovary than in the preceding stages, remaining in contact with 

 the anterior end of the irregular mass of medullary cords. The rete 

 ovarii and rete testis now follow different courses of development. 



13 cm. Embryo. Male. — The cords of the rete testis have in 

 most cases undergone a process of lumen formation. This is brought 

 about by the drawing apart of the cells from the axis of the cords. 

 As already shown, these rete cells are attached to the ensheathirrg 

 membrana propria, hence the lumen is formed by a very simple pro- 

 cess by which they are made to separate along the line of greatest 

 weakness (axis of cord). These rete tubules branch and anastomose 

 quite like the seminiferous tubules. Their homology to the latter is 

 still more clearly shown by the great similarity in the component cells 

 of the two structures. 



The rete tubules contain a few primitive sex cells (Plate VI, Fig. 21) 

 exactly like those found in the seminiferous tubules. These are 

 nothing new, as we have seen them to occur in the rete tubules of the 

 very earliest stages. Another point of similarity is found in the char- 

 acter of the epithelial cells of the rete tubules which are in every 

 regard similar to the germinative cells of the seminiferous tubules. 

 Transition forms between epithelial cells and primitive sex cells do 

 not exist in the former, while they are quite plentiful in the latter. 



The rete tiibules send out side branches (tubuli recti) that fuse with 

 the inner ends of the seminiferous tubules. In this manner one rete 

 tubule may come into direct connection with a large number of semin- 

 iferous tubules. In one section, a rete tubule was seen to send out 

 four tubuli recti connecting with as many seminiferous tubules. The 

 point of Junction of tubulus rectus and seminiferous tubule (Plate V, 

 Fig. 18) is easily recognized by the difference in diameter of the two 

 elements, by the difference in arrangement of their component cells 

 and by the presence of a lumen in the rete tubules as contrasted with 

 the absence of such in the seminiferous tubules. In cases where con- 

 nection has not been completely established between these two struc- 



