Bennet Mills Allen 95 



rapid multiplication of its cells. On the other hand the stroma cells 

 divide with far less frequency. 



As might be expected from the above, the stroma cells are 

 practically identical with the peritoneal cells from which they are 

 originating. In general their nuclei tend to assume a more rounded 

 shape. 



Here and there in both peritoneum and stroma one finds cells quite 

 different from those described above. These have clearly marked 

 boundaries, lightly staining cytoplasm, a centrosphere and a centro- 

 some. The large, round nucleus contains prominent nucleoli, usually 

 two in number, and also a chromatin network of slender strands quite 

 different in appearance from the rather granular irregular chromatin 

 masses of the peritoneal and stroma nuclei. These primitive ova are 

 so rare that one must hunt through as many as seven or eight sections 

 in order to find one. They divide by mitosis, as a result of which 

 division they are found to occur in small groups. 



The inner boundary of the mesenchymal portion of the sex gland 

 rudiment is formed by the capsules of the Malpighian corpuscles. The 

 component cells of the capsules resemble those of the stroma in their 

 lack of definite boundaries and in the character of their nuclei, being 

 distinguished from the latter chiefly by the darker color of their cyto- 

 plasm. 



The rudiment of the rete (Plate I, Fig. 2) is essentially like the sex 

 gland rudiment save for the fact that the basement membrane of the 

 peritoneum is somewhat less distinct in the former than in the latter 

 and the primitive ova are not quite so numerous; these differences are 

 probably due to the fact that the tissue of the sex gland rudiment is 

 more dense than that of the rete rudiment. 



0.8 cm. Embryo. — In this stage, the mesonephros is found to have 

 almost doubled in size; for this reason there has been little thickening 

 of the rete and sex gland rudiments. The number of primitive ova 

 has greatly increased and many clear cases of mitosis are found among 

 them. The basement membrane of the peritoneal layer has become 

 roore clearly defined in both rete and sex gland rudiments, yet it is 

 still broken in spots where cells are being proliferated into the under- 

 lying stroma, sometimes forming chains of two, three or four cells. 



1.0 cm. Embryo. — The mesonephros has become half again as broad 

 in this stage as in the preceding one, and has also increased in the 

 dorso-ventral dimension. 



The rete rudiment has not grown in thickness, yet the peritoneal 

 cells are seen to be rapidly dividing by mitosis. This results in a 



