1158 MALE GENERATIVE ORGANS. 



mediastinum. Each lobule is contained in one of the intervals between the fibrous 

 cords and vascular processes which extend between the mediastinum testis and 

 the tunica albuginea, and consists of from one to three or more minute convoluted 

 tubes, the tubuli seminiferi. The tubes may be separately unravelled by careful 

 dissection under water, and may be seen to commence either by free cgecal ends or 

 by anastomotic loops. The total number of tubes is considered by Munro to be 

 about 300, and the length of each about sixteen feet ; by Lauth their number is 

 estimated at 840, and their average length two feet and a quarter. The diameter 

 varies from 2-^- to yi^- of an inch. The tubuli are pale in color in early life, but 

 in old age they acquire a deep yellow tinge from containing much fatty matter. 

 They consist of a membrana propria, inside which are several layers of epithelial cells, 

 the seminal cells. The membrana propria is a hyaline structure, consisting of several 

 membranous layers, containing oval flattened nuclei at regular intervals, super- 

 imposed on one another. The seminal cells or lining epithelium differ in different 

 tubules. In some tubes they may be seen to consist of an outer layer, next the 

 membrana propria, and two or more layers of inner cells. The former cells are 

 more or less polyhedral in shape, uniform in size, and contain an oval or spherical 

 nucleus ; the latter cells, those comprising the inner layers, are spherical and more 

 loosely connected together. The nucleus of most or all of them is in the process 

 of indirect division (karyokinesis, page 40), and in consequence of this numerous 

 small spherical daughter-cells are to be seen, lying nearest to the lumen and closely 

 connected together. These small daughter-cells are named spermatoblasts, and by 

 -a series of changes become converted into spermatozoa. In other tubes the gradual 

 transition of the spermatoblasts into spermatozoa may be traced. In some tubes 

 or parts of tubes the daughter-cells may be seen to have assumed a pear shape, 

 with the pointed end, in which the nucleus is to be found, directed toward the 

 inner seminal cells, while the broad part is directed into the lumen of the tube. 

 In other parts of a tube the broad end may be seen to have become elongated into 

 a rod-shaped body, which constitutes the middle piece of the spermatozoon, Avhile 

 the nucleus forms the head. Again, in other parts of the tubes these young 

 spermatozoa may be seen collected together into fan-shaped groups, and from their 

 distal -end that is to say, the end projecting into the lumen of the tube a thin 

 long filament, called the tail, is growing out. In the young subject the seminal 

 cells present somewhat the appearance of an epithelial lining, and do not almost 

 fill the tube, as in the adult testis. % 



The tubules are enclosed in a delicate plexus of capillary vessels, and are held 

 together by anintertubular connective tissue, which presents large interstitial spaces 

 lined by endothelium, which are believed to be the rootlets of lymphatic vessels 

 of the testis. 



In the apices of the lobules the tubuli become less convoluted, assume a nearly 

 straight course, and unite together to form from twenty to thirty larger ducts, of 

 about -^ of an inch in diameter, and these, from their straight course, are called 

 vasa recta or tubuli recti. 



The vasa recta enter the fibrous tissue of the mediastinum, and pass upward 

 and backward, forming, in their ascent, a close network of anastomosing tubes, 

 which are merely channels in the fibrous stroma, having no proper walls ; this 

 constitutes the rete testis. At the upper end of the mediastinum the vessels of 

 the rete testis terminate in from twelve to fifteen or twenty ducts, the vasa 

 efferentia : they perforate the tunica albuginea, and carry the seminal fluid from 

 the testis to the epididymis. Their course is at first straight ; they then become 

 enlarged and exceedingly convoluted, and form a series of conical masses, the coni 

 vasculosi, which, together, constitute the globus major of the epididymis. Each 

 cone consists of a single convoluted duct from six to eight inches in length, the 

 diameter of which gradually decreases from the testis to the epididymis. Oppo- 

 site the bases of the cones the efferent vessels open at narrow intervals into a 

 single duct, which constitutes, by its complex convolutions, the body and globus 

 minor of the epididymis. When the convolutions of this tube are unravelled it 



