Bennet Mills Allen 111 



criteria noted in the pig embryo. Both rete and sex regions are found 

 to contain them. 



lJ^y2-Day Embryo. — At this stage the sex gland rudiment is easily 

 distinguishable from the rete portion of the genital ridge. It is hemi- 

 spherical in transverse section, having attained a marked increase in 

 height over the preceding stage by multiplication of the cells of the 

 peritoneum and of the stroma cells which are manifestly derived from 

 it. Sex cords are well formed, as in the 1.4 cm. stage of the pig, being 

 likewise continuous with the peritoneum from which they were formed 

 by a process of invagination. Although the cords appear with a fair 

 degree of clearness, the rabbit is by no means so favorable a subject 

 for the determination of the manner of their formation, as is the pig. 



The rete portion of the genital ridge is quite low in comparison with 

 the rudiment of the sex gland. Here one finds certain scattered 

 diffuse cords projecting from the peritoneum into the. underlying 

 stroma, each invested by a membrana propria continuous with the 

 basement membrane of the peritoneum. There are a few primitive 

 sex cells in these rete tubules, but the predominating type of cells 

 comprises those with small, oval, deeply-staining nuclei without cell 

 boundaries, such as compose the peritoneum. These cells are attached 

 to the membrana propria or basement membrane, as the case may be, 

 by slender strands of cytoplasm, showing the same relation in this 

 regard as do the corresponding cells in the pig embryo. 



The nuclei of the stroma in both rete and sex gland rudiments are 

 found to be irregular in shape, giving the appearance of undergoing 

 division by amitosis. 



16-Day Embryo. — The rete tubules of the region anterior to the 

 sex gland can be readily detected. They lie in a mass triangular in 

 transverse section. This is limited by the mesentery of the mesone- 

 phros, the capsules of Bowman and the peritoneum. In places the 

 rete tubules can be seen growing in from the peritoneum and branch- 

 ing in the stroma. Each has a rudiment of a lumen which opens into 

 the body cavity on the one hand, and on the other extends for a short 

 distance into the interior of the tubule. These rete tubules can be found 

 along the entire length of the rete rudiment and back beneath the sex 

 cords of the rudimentary sex gland. In this region — the anterior end of 

 the sex gland — it is difficult to distinguish the rete tissues from the under- 

 lying layer of connective tissue cells that separates them from the 

 Malpighian corpuscles. The rete nuclei differ from those of overlying 

 sex cords in that they are slightly smaller, more irregular and more 

 deeply-stained than the latter. These rete nuclei are not to be dis- 



