DEVELOPMENT OF OVARY AND TESTIS. 57 



apart than do the sex-cords, and penetrate more deeply into the 

 mesenchyme. Both rete-cords and sex-cords are at this stage 

 devoid of a lumen. In cross-section they show a limiting mem- 

 brana propria, within which is a single layer of cells arranged 

 with their bases attached to the membrana propria and their 

 apices meeting at a common point in the center the rudiment 

 of the lumen. 



The mesentery of the sex gland is formed by the proliferation 

 of connective tissue cells from the peritoneum, in areas of re- 

 stricted width immediately ventral and dorsal to the sex gland. 

 The ventral area is by far the more important of the two sources. 

 The albuginea is in large part formed from the cells comprising 

 the proximal parts of the sex-cords. They are formed at the 

 time when the sex gland has begun to assume definite shape. 

 At this time the rapidly dividing cells of the attached ends of the 

 sex-cords have become differentiated from those of the more 

 distal portions in that they elongate, become smaller, and acquire 

 the property of staining more deeply. They then break away 

 from the peritoneum on the one hand, and from the sex-cords on 

 the other. They may still for some time be found attached to 

 portions of the membrana propria that ensheathed them. They 

 become mingled with certain exactly similar intertubular mesen- 

 chymal elements, to form the albuginea, which is essentially one 

 with the remaining connective tissue or stroma of the sex gland. 

 Sexual differentiation is first manifested by the cessation of growth 

 of the sex-cords of the ovary. We can then distinguish them as 

 medullary-cords. The peritoneum of the ovary begins to in- 

 crease in thickness, and eventually forms the cortex of the adult 

 ovary in a manner to be briefly indicated below. The albuginea 

 of the ovary forms a broader, looser, and more irregular layer 

 than does that of the testis. In the testis the peritoneum ceases 

 to grow, in large measure at least, its cells becoming flattened, 

 and in later life practically disappearing. The rete cords grow 

 backwards from their points of origin, and enter the anterior 

 part of the sex gland. They branch and anastomose through- 

 out their course, sending branches to the Malpighian corpuscles 

 on the one hand, and on the other to the seminiferous tubules of 

 the testis. The branches passing to the Malpighian corpuscles 



