THE TESTICLES AXD THEIR COVERINGS 1383 



nucleus of the former 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 strata; 

 these are the spermatocytes of the first order, or mother cells. Most of the cells are in a con- 

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

 layer, the spennatocytes of the second order, or daughter cells. (3) The latter by division 

 give rise to the spermids, which change into the spermia or spermatozoa. 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 spermia proceeds, the 

 latter group themselves around the inner extremities of the supporting cells. The nuclear part of 

 the spermid, which is partly embedded in the supporting cell, is differentiated to form the head 

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

 and tail, the latter projecting into the lumen of the tube. Ultimately the heads are separated 

 and the spermia are set free. 



The process of spermatogenesis bears a close relation to that of maturation of the ovum. 

 The spermatocyte is equivalent to the immature ovum. It undergoes subdivision, and ulti- 

 mately gives origin to four spermia, each of which contains, therefore, only one-fourth of the 

 chromatin elements of the nucleus of the spermatocyte (see Ovum, p. 1402). 



CREMASTCft 



ANASTOMOSIS 

 OF VEINS 



FIG 1133 Vaginal tunics of the testicle. (Poirier FIG. 1134. Ligament of the scrotum or guber- 



and Charpy.) nuculum testis. (Poirier and Cnarpy.) 



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

 intertubular connective tissue, which presents large interstitial spaces lined by endothelium, 

 which are believed to be the rootlets of lymphatic vessels of the testis. In this interstitial tissue 

 are groups of large granular cells, the interstitial cells. These contain pigment, fat, and crystal- 

 loids, and are more numerous before and after sexual activity. 



The aberrant ducts of the epididymis (ductuli aberrantes) are tortuous and end in blind ex- 

 tremities. The superior aberrant duct (ductus aberrans superior) is in the globus major and 

 joins the rete testis. The inferior aberrant duct (ductus aberrans inferior) (Fig. 1132) is in the 

 tail of the epididymis, and takes origin from the duct of the epididymis or the seminal duct. It 

 is a persistent canal of the Wolffian body. It extends up the cord for two or three inches and 

 terminates by a blind extremity, which is occasionally bifurcated. It may be as much as fourteen 

 inches in length when unravelled. Its structure is similar to that of the vas deferens. 



The descent of the testis will be described on page 1426. 



The Semen. The semen is the viscid, whitish, or opalescent fluid, of alkaline 

 reaction and characteristic odor, which is secreted by the testes, prostate, seminal 

 vesicles, and Cowper's glands. It contains water and about 18 per cent, of solid 

 matter, chiefly consisting of proteids, salts, and nitrogenous substances. The 

 semen serves to convey and maintain the vitality of the spermia in their course 

 a bug the seminal passages. 



The Spermatozoa, or Spermia, are present in enormous numbers in the seminal 

 fluid. Each consists of a head, neck, body, and tail. 



