DEVELOPMENT OF THE REPRODUCTIVE ORGANS. 



2039 



Globus major 



the germinal ridge by the underlying mesoblastic stroma, whereby the epithelial 

 mass becomes broken up into cylinders and cords that extend into the subjacent 

 stroma. The cell-cords are composed of two kinds of elements, the numerous chief 

 epithelial cells and the larger sperm-cells, the direct descendants of the indiffer- 

 ent primary germ-cells, which they embrace. About the fifth week a layer of 

 mesoderm insinuates itself between the superficial and deeper portions of the epi- 

 thelial mass, thereby separating a peripheral zone. This ingrowth results in the 

 formation of a robust fibrous envelope, the tunica albuginea, around the entire testis, 

 while the separated mesothelial layer differentiates into the serous covering. The 

 cell-cords become subdivided by the ingrowth of the mesoblastic stroma into smaller 

 spherical masses, which subsequently are converted into the seminiferous tubules, 

 while from the stroma are supplied the interlobular septa and the intralobular support- 

 ing tissue. About the sixth week additional cell-cords grow into the young testis 

 from the adjacent Wolffian tubules. These 



ingrowths invade the attached border of Fig. 1718. 



the testicle and become the viedullary 

 cords, which are so disposed that each 

 comes into relation with one of the spheri- 

 cal epithelial cell-masses. Although both 

 the latter and the medullary cords are 

 solid, the later relation of the secreting 

 tubules of the gland to the excretory 

 channels is thus. foreshadowed, since from 

 the ingrowths from the Wolffian tubules 

 are derived the straight tubules and those 

 of the rete testes. The farther differen- 

 tiation of the seminiferous canals, which, 

 as well as the medullary cords, arc with- 

 out lumen until near puberty, proceeds 

 from the growth and branching of the cell- 

 masses, the cells of which become the epi- 

 thelium of the tubules. The latter are 

 enclosed by an investment of condensed 

 mesoblastic stroma continuous with the 

 supporting tissue and framework of the 

 gland. At the approach of sexual ma- 

 turity the primary sperm-cells within the 

 tubules proliferate and become the sperma- 

 togonia, while from other epithelial ele- 

 ments are derived the Sertoli cells. The 

 roles played by these elements in the pro- 

 duction of the spermatozoa are described 

 under Spermatogenesis (page 1945). 



Coincidently with the growth of the 

 testis the Wolffian body atrophies, with the exception of some of its tubules and duct, 

 which increase and, in conjunction with the medullary cords also derived from the 

 mesonephros, establish the elaborate excretory passages of the sexual gland. From 

 the Wolffian tubules are developed the coni vasculosi and the ductuli efferentes, while 

 the Wolffian duct gives rise to the tube of the epididymis, the vas deferens, and, as 

 a secondary outgrowth, the seminal vesicle. The caudal group of mesonephric tubules 

 are represented in both sexes by rudimentary structures, which in the male are the 

 paradidymis and the vasa aberrantia. The appendix of the epididymis, or stalked 

 hydatid, probably also owes its origin to the Wolffian duct. 



Although, as is evident from the foregoing, the Wolffian tubules and duct are 

 largely concerned in the development of the generative tract in the male, the Miil- 

 lerian duct is not without representation, since its two extremities persist. The 

 upper (after migration lower) end remains as the appendix of the testis, and the 

 lower, fused with its fellow, is seen as the prostatic utricle, which, therefore, is the 

 homologue of the vagina and, possibly, the uterus. In exceptional cases, where it 



Rete testis 



Duct of 

 epididymis 



Seminiferous 

 tubes 



Fibrous 

 capsule 



Globus minor 



Ligamentum stiotale v ' "" 



■\ 



Longitudinal section of developing testicle. X 20. 



