Bennet Mills Allen 101 



It is significant to note that one finds here certain transition forms 

 which link the usual type of peritoneal cells with the primitive sex 

 cells found in the sex cords. In some cases these transition nuclei 

 show much the same characters as regards chromatin and nucleolus 

 as do the nuclei of the primitive sex cells, yet they differ in shape and 

 size. It should be noted, in this connection, that the peritoneal layer 

 is almost completely separated from the sex cords by the albuginea. 



There are numbers of spherules of fat in the peritoneum covering 

 the sex gland. These evidently indicate a process of fatty degenera- 

 tion that seems to attack the cytoplasm of the cells and later to de- 

 stroy a few of the nuclei, resulting in giving to the peritoneum a 

 ragged appearance, there being large gaps where the cells have been 

 destroyed. 



2.5 cm. Embryo. — Sex differentiation is very strikingly shown in 

 this most important stage. In the testis the albuginea has become 

 thicker and denser than in the preceding stage. At the same time, 

 the peritoneum has become flattened and is definitely separated from 

 the albuginea by a distinct basal membrane. It contains no primi- 

 tive sex cells. The peritoneal covering (germinal epithelium) of the 

 ovary has become thickened and has even begun to send a few slender 

 cords of cells into the loose underlying albuginea. These are the 

 cords of Pflliger. They are, in many cases, loosely connected with the 

 ovarian sex cords which we shall hereafter designate as medullary 

 cords. 



The process of fatty degeneration noted in the peritoneum of the 

 preceding stage is still taking place in both ovary and testis, and has 

 even extended to the sex cords in which large numbers of fat spherules 

 appear. These occur almost exclusively in the syncytial cytoplasm 

 of the germinative cells. They are most numerous in the portion of 

 the sex cords furthest from the mesentery. Their fatty nature seems 

 pretty evident from the fact that they are stained black by osmic acid 

 and also from the spherical form that they assume. 



The medullary cords are quite shrunken, being in most part clumped 

 together in an irregular mass lying near to the mesentery. Cell de- 

 generation occurring in them is not balanced by sufficiently rapid cell 

 division. The primitive sex cells are surrounded by the undifferen- 

 tiated cells that we have been terming germinative cells. This term, 

 however, should henceforth be applied strictly to these cells in the 

 seminiferous tubules alone. All resemblance to a tubular condition 

 is lost, the medullary cords appearing in the form of masses of cells 

 with no evidence of a very regular arrangement. 



