123 Embryonic Development of Ovary and Testis of Mammals 



moving outward, and at the same time adding to the cords already laid 

 down, by a continuation of the invagination process. 



These cords are truly of a tubular nature, a lumen, though not present, 

 being conditioned by the arrangement of the cells. Transverse sections 

 of these incipient tubules show a bounding meml)rana propria which is 

 continuous with the basement membrane of the peritoneum. Inside of 

 this is a single layer of peritoneal cells with their bases attached to the 

 membrana propria, while their apices meet at a common central point — 

 the rudiment of the future lumen. 



The invaginations are much fewer in the rete region than in the sex 

 gland rudiment, and also differ from those of the latter region in the 

 fact that they penetrate through the stroma to the walls of the Malpighian 

 corpuscles (Plate II, Fig. 6), from which the rudimentary sex cords 

 are separated by a layer of stroma. The limit between the rete and sex 

 gland rudiments may be roughly placed at a point opposite the 12th 

 glomerulus, in the rabbit, and opposite the 20th, in the pig ; however, the 

 sex gland rudiment slightly overlaps the rete region; hence the impossi- 

 bility of drawing a sharp limit between the two. 



There has been a great diversity of opinion in regard to the origin 

 of the sex cords and rete tubules. Practically all writers except Egli, 

 Janosik, Coert and von Moller have derived the rete tubules from the 

 Malpighian corpuscles. The above named, considered them as products 

 of the peritoneum covering the mesonephros. There has been greater 

 unanimity in regard to the derivation of the sex cords. We shall not 

 enter into detail upon this subject, but shall simply point out the fact 

 that Waldeyer, 70 and 02, Kolliker, 98, Balfour, 78, Rouget, 79, and 

 others hold that the sex cords arise from the Malpighian corpuscles, and 

 that they receive primitive sex cells which migrate to them from the peri- 

 toneum. 



According to Mihalkovics, 85, the cells of the sex cords arise from the 

 germinal epithelium, not through direct invagination but in an indirect 

 manner, through infiltration of the stroma by peritoneal cells which later 

 become segregated to form strands. 



Schulin, 81, and Coert, 98, hold a somewhat different view, namely 

 that the entire sex gland is formed from a homogeneous mass of cells 

 blastema) derived from the peritoneum. This view differs from that 

 of Mihalkovics, 85, in that the latter does not consider the stroma to be 

 derived from the peritoneum, while Coert considers such a peritoneal 

 origin of the stroma to be very probable, and extends this idea to 

 explain the formation of the rete tubules and the sex cords as well. 



The continued growth of the sex cords at their bases and the accom- 



