Bennet Mills Allen 103 



formation of these cells apparently affects both rete and sex gland at 

 the same time. It is barely possible that the presence of fatty 

 spherules so evident in the 2.5 cm. stage may be in some manner cor- 

 related with the active formation of primitive sex cells in the seminife- 

 rous tubules, cords of Pfliiger and rete cords, all of which structures 

 have been shown to be homodynamous. Such a hypothesis would, how- 

 ever, require more evidence for its proof than we have yet found. 



The fat globules so numerous in the sex gland of the 2.5 cm. em- 

 bryo have almost entirely disappeared from all save the interstitial 

 cells of the testis, in the fat globules of these there has been an increase 

 which may or may not be correlated with their disappearance in the 

 seminiferous tubules. Whatever loss of cells may have taken place in 

 the serniniferous tubules at the preceding stage has been compensated for 

 by a process of rapid cell division. This, together with the transfor- 

 mation of germinative cells, has resulted in a decided increase in the 

 number of primitive sex cells. 



The peritoneum of the testis has become still further flattened, and 

 its fatty spherules have almost wholly disappeared. 



The albuginea nuclei have become more attenuated than in pre- 

 vious stages, yet they do not differ essentially from certain other con- 

 nective tissue elements of the stroma, many of the more attenuated 

 of which are seen to become applied to the membrana propria of the 

 seminiferous tubules in such a manner as to form thin connective 

 tissue sheaths. 



The interstitial cells are an extremely important constituent of the 

 testis, occupying the interspaces between the seminiferous tubules 

 (see Plate IV, Fig. 13). In the ovary, on the other hand, they are 

 very sparse. In the place of them one finds great masses of loose 

 connective tissue, filling the interspaces between the other ovarian 

 tissues. 



3.5 cm. Embryo. — This stage will be noted chiefiy to record the reduc- 

 tion in the cytoplasm of the interstitial cells of the ovar}^ jSTot only 

 has the cytoplasm of these sparse cells become shrunken, but the cen- 

 trosome and centrosphere have almost disappeared. Both primitive 

 sex cells and follicle cells of the medullary cords are suffering exten- 

 sive degeneration. This continued process of degeneration is even 

 more marked in the cortex and cords of Pfliiger, which are now just 

 beginning to assume importance. 



4- cm. Embryo. — There is an interesting process of karyolytic de- 

 generation that appears in the rete cords of this stage. The chro- 

 matin of the nuclei so affected gathers together in a rounded solid 



