Bennet Mills Allen 105 



Fatty degeneration has almost ceased in the medullary cords and 

 cords of Pfliiger. 



7.5 cm. Embryo. Ovary. — A few of the ^:x cells ct the cords of 

 Pfliiger have undoubtedly developed into the condition of oocytes 

 because of the fact that their chromatin threads have taken on the 

 synapsis form described by Winiwarter, oo, in the rabbit. Corr'3S- 

 ponding synaptic stages are also found in the medullary cords, thus 

 bringing out the close homology of the two structures. 



The cords of Pfliiger have become elongated and have at the same 

 time branched and anastomosed to form a network in a manner quite 

 like that of the seminiferous tubules in the testis. The resemblance 

 is still further heightened by the fact that the cords of Pfliiger are 

 invested with a connective tissue layer formed by attenuated con- 

 nective tissue cells of the stroma. The same is true of the medullars- 

 cords. 



We might homologize these three structures by considering the 

 seminiferous tubules and medullary cords as exactly homologous struc- 

 tures, while the cords of Pfliiger constitute a second series of invagina- 

 tions in all respects homologous with the medullary cords save as re- 

 gards the time of origin. 



Testis. — The structure of the testis is essentially the same as in 

 earlier stages. There has been a progressive increase in the extent of 

 the system of seminiferous tubules, which has been brought about by 

 the continued growth and branching of those already laid down pre- 

 vious to their separation from the peritoneum (1.7 cm. embryo). The 

 nuclei of the germinative cells are attached to the basement mem- 

 brane by strands denser than the surrounding cytoplasm. This rela- 

 tion to tlie basement membrane is exactly similar to that of the peri- 

 toneal cells in the earliest stages (0.7 cm. embryo). The primitive 

 sex cells are increasing in number by two processes, namely: (1) 

 division by mitosis of those already present in earlier stages; (2) trans- 

 formation of germinative cells into sex cells. All stages in this trans- 

 formation process can be noted, any transverse section of the testis at 

 this stage (Plate IV, Fig. 14) showing a complete series of transition 

 forms. The same may be seen in embiyos earlier and later than this, 

 namel}', from 3 cm. to 13 cm. in length. Primitive sex cells occur in 

 the rete cords of both male and female, those of the male being ap- 

 parently in the same stage of development as are those of the semin- 

 iferous tubules. This is not true in the female at this stage, owing 

 to the fact that the primitive sex cells of the cords of Pfliiger and 

 medullary cords have developed precociously, outstripping those of 

 the rete ovarii. 

 9 



