DEVELOPMEST OF THE TESTES 



235 



imiiieroiis follicles, continue unbroken in the testis to form semin- 

 iferous cords in which a lumen later occurs and seminiferous tubules 

 result. The mesenchyme between the tubules forms thin walls 

 al)out them and also sei)ta se])aratino; the organ into com])artments 

 called lobules. The septa connect with the sheath of connective 

 tissue surroundino; the testis. (Fig. 14().) 



When the early ei)ithelial mass forms cords of cells, two types of 

 cells become distinguishable. Of these, the greater number are 

 small polyhedral or cuboidal, and among them are fewer larger, 

 more or less spherical primitive sex cells with large nuclei. Some 



Fig. 146. — Diagram of the seminiferous tubules and rete testis of a mammal. 



observers correlate the small cells with the follicle cells surroimding 

 the ova in a developing ovary and the large cells with the ova. 



When the testis is mature, two types of cells, namely, spermato- 

 togonia and Sertoli cells, are the main components of the tubules. 

 Spermatogonia, which will give rise to spermatozoa, are believed to 

 be descendants of the large primitive sex cells, and the cells of 

 Sertoli are thought to develo]) from the small cells corresponding to 

 ovarian follicle cells. However, there are repeated cycles of cell 

 degeneration and proliferation in these seminiferous tubules, and, 

 according to some investigators, the early sex cells are lost in the 

 process and the spermatogonial cells of the fimctional testis are 

 derived from the original small follicle cells that survive. In either 

 case, spermatogonial cells alternate in location with Sertoli cells 



