[CHAPTER VII]
THE FUNCTION OF THE MALE GENERATIVE ORGANS
Testicles.—The function of the testicles is threefold. There is first the inner secretion of certain substances, spermines, which are the cause of the male secondary characteristics. Eunuchs who have been operated upon before puberty show feminine traits in their appearance throughout their lives. They have sloping shoulders, flabby muscles, beardless faces, high-pitched, squeaky voices and festoons of fat on breasts and hips. Secondly, certain stimuli starting from the testicles serve to increase the tonus of the centres of erection. The main function of the testicles is the production of spermatozoa.
CUT XXX.
Spermatogenesis.
1, basement membrane; 2, Sertoli’s or sustentacular cell; 3, spermatogone; 4, spermatocytes; 5, spermatids; 6, heads of spermatozoa.
Spermatogenesis.—The testicles belong to the class of tubulous glands. The tubules are through the greater part of their course convoluted, tubuli contorti, toward the end they become straight, tubuli recti. The wall of the convoluted tubules consists of three layers, (1) an external connective tissue layer, (2) a middle basement membrane, and (3) interiorly, an epithelial lining. The epithelium consists of two kinds of cells, first the supporting or the sustentacular or Sertoli’s cells and secondly the glandular cells.
When in activity, the glandular cells show three different strata, which represent the three different stages of spermatogenesis. The first stratum, the spermatogones, lie against the basement membrane. They soon begin to increase by cell division and move toward the centre of the tubule. During this movement they increase in size and show the different stages of mitotic division. These enlarged cells are called spermatocytes and form the second stratum. The cells produced by the mitosis of the spermatocytes constitute the third stratum and are called spermatids.
During the transformation of the spermatocyte into a spermatid a reduction of its chromosomes to one-half the number, specific for the species, takes place. This reduction represents the maturition of the sperm-cell, when the segregation of the unit characters is effected. A spermatid is, therefore, already a gamete, i. e., a reproductive cell in the reduced condition.
The spermatids are small round cells which line the lumen of the seminiferous tubules. The spermatids soon become ovoid. The nucleus forms the head, and the cytoplasm is drawn into a tail-like processus. In this stage the spermatids are called spermatozoa. A Sertoli’s cell, together with a group of developing spermatozoa attached to its central end, is called spermatoblast.
The epithelium of the tubuli contorti thus consists of three strata, first of the stratum of the spermatogones, lying against the basement membrane, secondly of the stratum of spermatocytes which are spermatogones in the state of mitosis, and thirdly of the stratum of spermatids which are transformed spermatocytes. The spermatozoa are spermatids which have assumed their permanent shape.