D. THE MALE GENITAL ORGANS.

1. THE SPERMATOZOON.

The semen, or sperma, is a fluid that, as a whole, consists of the secretion of several sets of glands in which the sexual cells, the spermatosomes, or spermatozoa, which are formed in the testes, are suspended.

We shall first consider the structure of the typical adult spermatosome, taking up consecutively its component parts. Three principal parts may be distinguished-the head, the middle piece, and the tail or flagellum. The round or oval body of the head terminates in a lanceolate extremity. The former consists of chromatin, and is most intimately associated with the phenomenon of fertilization. The middle piece, which is attached to the posterior end of the head, is composed of a protoplasmic envelop which surrounds a portion of the so-called axial thread. The latter is enlarged anteriorly just behind the head to form the terminal nodule, which fits into a depression in the head. From the middle piece on, the axial thread

h

k b

n

m

Fig. 271.-Diagram showing the general characteristics of the spermatozoa of various vertebrates: a, Lance; b, segments of the accessory thread; c, accessory thread; d, body of the head; e, terminal nodule; ƒ, middle piece; g, marginal thread; h, axial thread; i, undulating membrane; k, fibrils of the axial thread; 7, fibrils of the marginal thread; m, end piece of Retzius; n, rudder-membrane.

is continued into the tail of the spermatozoon, and is here surrounded by a transparent substance—the sheath of the axial thread. The envelop is lacking at the posterior extremity of the tail, where the axial thread extends for a short distance as a naked filament called the end-piece of Retzius. From the middle piece a still finer thread is given off, the marginal thread, which extends at a certain distance from the axial thread as far as the end-piece of Retzius. In its course it crosses and recrosses the axial thread at various points, and may even wind around it in a spiral manner. In all instances it is connected with the sheath of the axial thread by a delicate membrane-the undulating membrane. Another and still more delicate filament-the accessory thread-runs parallel with the axial thread along the surface of its sheath and terminates at a certain distance from the end-piece of Retzius. Near the extremity of the flagellum and immediately in front of the end-piece is another and shorter membrane,—the rudder membrane,-which is continuous with the undulating membrane. Maceration reveals a fibrillar

a

b

structure of both the axial and marginal threads (Ballowitz), while the accessory thread is separated into a number of short segments. In mammalia, and especially in man, the spermatozoa seem to be more simply constructed. Here the head is pyriform, and somewhat flattened, with a slight ridge along the depression at either side of its anterior thinner portion (Fig. 272). In some mammalia (mouse), the head is provided with a socalled cap, which corresponds to the lance previously mentioned. The middle piece is relatively long and shows a distinct crossd striation, which may be attributed to its spiral structure. Here also the middle piece is traversed by the axial thread, which ends at the head in a terminal nodule, and may be separated as in other mammalia into a number of fibrils. Some years ago Gibbes described an undulating membrane in the human spermatozoon, an observation which was confirmed by W. Krause (81). The head of the human spermatosome is from 3 to 5 long, and from 2 to 3 μ in breadth; the middle piece is 6 long and I in breadth; the tail is from 40 μ to 60 μ long, and the end-piece 6u long. The spermatozoa are actively motile, a phenomenon due to the flagella, which give them a spiral, boring motion. They are characterized by great longevity and are very resistant to the action of low temperatures (vid. Piersol, 83). In some species of bat the spermatozoa penetrate into the oviduct of the female in the fall, but do not contribute to impregnation until the spring, when the ova mature. (For the structure of the spermatosomes see Jensen, Ballowitz.)

e

Fig. 272.-Human spermatozoa. The two at the left after Retzius (81); the one at the extreme left is seen in profile; the other in surface view; the one at the right is drawn as described by Jensen: a, Head; b, terminal nodule; c, middle piece; d, tail; e, end-piece of Retzius.

2. THE TESTES.

The testis is inclosed within a dense fibrous capsule,-the tunica albuginea,-about one-sixteenth of an inch in thickness, and surrounded by a closed serous sac, derived from the peritoneum during the descent of the testes, and therefore lined by mesothelial cells. This serous sac-the tunica vaginalis-consists of a visceral layer attached to the tunica albuginea, and a parietal layer which blends with the scrotum. The cavity contains normally a small amount of serous fluid. On the inner surface of the tunica albuginea is found a thin layer of loose fibrous tissue containing blood-vessels -the tunica vasculosa. The tunica albuginea is thickened in its

posterior portion to form the mediastinum testis, or the corpus Highmori, which projects as a fibrous-tissue ridge for a variable distance into the substance of the testis. The gross structure of the testis is best seen in a sagittal longitudinal section. Even a low magnification will show that the testis is composed of lobules. These are produced by septa which extend into the substance of the organ and are derived from the investing tunics of the testis and diverge in a radiate manner from the mediastinum testis. The lobules are of pyramidal shape, with their bases directed toward the capsule and their apices toward the mediastinum. They consist principally of the seminiferous tubules, whose transverse, oblique, and longitudinal

Fig. 273.-Longitudinal section through human testis and epididymis. The light areas between the lobules are the fibrous-tissue septa of the testis; X 2.

sections may be observed in sections of the testis. When isolated, these tubules are seen to begin in the testis as closed canals, which are closely coiled upon each other (convoluted tubules) and describe a tortuous course, until they finally reach the corpus Highmori. Immediately before they reach the latter, the convoluted tubules change into short, straight and narrow segments-the straight tubules, or tubuli recti. Within the corpus Highmori, all the straight tubules of the testis unite to form a tubular network-the rete testis (Haller).

From this network about fifteen tubules-the vasa efferentia

arise. The latter, at first straight, soon begin to wind in such a manner that the various convolutions of each canal form an independent system, invested by a fibrous sheath of its own-coni vasculosi Halleri. These lobules constitute the elements of the globus major of the epididymis. In cross-section the vasa efferentia are seen to be stellate in shape. The vasa efferentia gradually unite to form one canal—the vas epididymidis. This is markedly convoluted and is situated in the body and tail of the epididymis itself.

The epithelium of the convoluted seminiferous tubules consists of sustentacular cells (cells or columns of Sertoli) and of spermatogenic elements. The former are high, cylindric structures (see below), the basilar surfaces of which are in contact. They do not form a continuous layer, but their basal processes are interwoven to form a superficial network surrounding the epithelium of the

Sustentacular cells (cells of Sertoli) of the guinea-pig (chrome-silver method). Figure 274, surface view of the seminiferous tubules; figure 275, profile view; X 220: a, Basilar surface of a cylindric sustentacular cell; b, flattened sustentacular cell; ‹, c, depressions in the sustentacular cells due to pressure from the spermatogenic cells; d, basilar portion of sustentacular cells.

seminiferous tubules. (Fig. 275.) In the meshes of the reticulum are deposited numbers of plate-like cells, which lie in contact with the basement membrane and also represent sustentacular elements (vid. Merkel, 71).

Between the sustentacular cells are found from four to six rows of cells, possessing relatively large nuclei, rich in chromatin, and derived from cells of the deeper strata by mitotic cell division. The epithelium of the convoluted portion of the seminiferous tubules is, therefore, a stratified epithelium. The cells of this epithelium present various peculiarities according to their stage of development, and will be considered more fully in discussing spermatogenesis. Externally, the walls of the convoluted tubules are limited by a single layer or several layers of spindle-shaped, epithelioid cells. A basement membrane is present, but very thin, and in some cases

hardly capable of demonstration. The convoluted tubules are separated from each other by a small amount of connective tissue, in which, in addition to the vessels, nerves, etc., are found peculiar groups of large cells containing large nuclei, and known as interstitial cells. Nothing definite is known regarding the significance of these cells; but they are probably remains of the Wolffian body. Reinke (96) found repeatedly crystalloids of problematic significance in the interstitial cells of the normal testis.

The stratified epithelium of the convoluted tubules changes in

tubules.

the tubuli recti to an epithelium consisting of a single layer of short columnar or cubical cells resting on a thin basement membrane.

The canals of the rete testis (Haller) are lined by nonciliated epithelium, which varies in type from flat to cubical. Communicating with the rete testis is a blind canal, the vas aberrans of the rete testis, lined with ciliated epithelium.

The vasa efferentia are lined partly by ciliated columnar and partly by nonciliated cubical epithelium. The two varieties form groups which alternate, giving rise to nonciliated depressions, which represent gland-like structures (Schaffer, 92), but do not