THE TESTES. 1019 



of the gland, and is wider above than below. From the front and sides of this 

 septum numerous slender fibrous cords and imperfect septa (trabeculce) are given 

 off, which radiate toward the surface of the organ, and are attached to the inner 

 surface of the tunica albuginea. They therefore divide the anterior of the organ 

 into a number of incomplete spaces, which are somewhat cone-shaped, being broad 

 at their bases at the surface of the gland, and becoming narrower as they converge 

 to the mediastinum. The mediastinum supports the vessels and ducts of the testis 

 in their passage to and from the substance of the gland. 



The Tunica Vasculosa is the vascular layer of the testis, consisting of a plexus 

 of blood-vessels held together by a delicate areolar tissue. It covers the inner 

 surface of the tunica albuginea and the different septa in the interior of the gland, 

 and therefore forms an internal investment to all the spaces of which the gland is 

 composed. 



Structure. The glandular structure of the testis consists of numerous lobules 

 (lobuli testis). Their number, in a single testis, is estimated by Berres at 250, and 

 by Krause at 400. They differ in size according to their position, those in the 

 middle of the gland being larger and longer. The lobules are conical in shape, 

 the base being directed toward the circumference of the organ, the apex toward the 

 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 caecal 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 2-515- to y^-^- 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. 

 Each tube consists of a basement layer, formed of epithelioid cells united edge to 

 edge, outside which are other layers of flattened cells arranged in interrupted 

 laminae, which give to the tube an appearance of striation in cross section. The 

 cells of the outer layers gradually pass into the interstitial tissue. Within the 

 basement-membrane are epithelial cells arranged in several irregular layers, which 

 are not always clearly separated, but which may be arranged in three different 

 groups. Among these cells may be seen the spermatozoa in different stages of 

 development. 1. Lining the basement-membrane and forming the outer zone is 

 a layer of cubical cells, with small nuclei ; these are known as the lining cells or 

 spermatogonia. The nucleus of some of them may be seen to be in the process 

 of indirect division (karyokinesis), and in consequence of this daughter cells are 

 formed, which constitute the second zone. 2. Within this first layer is to be seen 

 a number of larger cells with clear nuclei, arranged in two or three layers ; these 

 are the intermediate cells or spermatocytes. Most of these cells are in a condition 

 of karyokinetic division, and the cells which result from this division form those 

 of the next layer, the spermatoblasts or spermatids. 3. The third layer of cells 

 therefore consists of the spermatob lasts or spermatids, and each of these, without 

 further subdivision, becomes a spermatozoon. They are ill-defined granular masses 

 of protoplasm, of an elongated form, with a nucleus which becomes the head of 

 the future spermatozoon. In addition to these three layers of cells others are seen, 

 which are termed the supporting cells, or cells of Sertoli. They are elongated and 

 columnar, and project inward from the basement-membrane toward the lumen of 

 the tube. They give off numerous lateral branches, which form a reticulum for 

 the support of the three groups of cells just described. As development of the 

 spermatozoa proceeds the latter group themselves around the inner extremities of 

 the supporting cells. The nuclear part of the spermatozoon, which is partly 

 imbedded in the supporting cell, is differentiated to form the head of the spermato- 

 zoon, while the cell protoplasm becomes lengthened out to form the middle piece 



