. Principles of modern biology. Biology. Reproduction in Multicellular Animals - 385 INTERSTITIAL CELLS SPERMATOGONIA MATURE SPERM SERTOLI CELL Fig. 21-7. Cross section of a sperm-forming tubule of the human testis (semidiagrammatic). carry the sperm into the epididymis (Fig. 21-6), a part of the genital tract that is de- rived from an embryonic kidney. The epi- didymis in man has the appearance of a compact mass that half encircles the testis (Fig. 21-5), but actually the epididymis is a very long (about 20 feet), much-coiled tube that leads finally into the vas deferens, or sperm duct proper

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. Principles of modern biology. Biology. Reproduction in Multicellular Animals - 385 INTERSTITIAL CELLS SPERMATOGONIA MATURE SPERM SERTOLI CELL Fig. 21-7. Cross section of a sperm-forming tubule of the human testis (semidiagrammatic). carry the sperm into the epididymis (Fig. 21-6), a part of the genital tract that is de- rived from an embryonic kidney. The epi- didymis in man has the appearance of a compact mass that half encircles the testis (Fig. 21-5), but actually the epididymis is a very long (about 20 feet), much-coiled tube that leads finally into the vas deferens, or sperm duct proper Stock Photo
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. Principles of modern biology. Biology. Reproduction in Multicellular Animals - 385 INTERSTITIAL CELLS SPERMATOGONIA MATURE SPERM SERTOLI CELL Fig. 21-7. Cross section of a sperm-forming tubule of the human testis (semidiagrammatic). carry the sperm into the epididymis (Fig. 21-6), a part of the genital tract that is de- rived from an embryonic kidney. The epi- didymis in man has the appearance of a compact mass that half encircles the testis (Fig. 21-5), but actually the epididymis is a very long (about 20 feet), much-coiled tube that leads finally into the vas deferens, or sperm duct proper
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. Principles of modern biology. Biology. Reproduction in Multicellular Animals - 385 INTERSTITIAL CELLS SPERMATOGONIA MATURE SPERM SERTOLI CELL Fig. 21-7. Cross section of a sperm-forming tubule of the human testis (semidiagrammatic). carry the sperm into the epididymis (Fig. 21-6), a part of the genital tract that is de- rived from an embryonic kidney. The epi- didymis in man has the appearance of a compact mass that half encircles the testis (Fig. 21-5), but actually the epididymis is a very long (about 20 feet), much-coiled tube that leads finally into the vas deferens, or sperm duct proper. The vas deferens is a relatively simple tube, with a thick muscular wall, that leaves the scrotum and passes into the abdominal cavity, through the inguinal canal. In the abdominal cavity, the vas deferens ends by joining the urethra, a short stout tube that originates from the urinary bladder. Thus the urethra fulfills a double duty, in that it conveys both urine and semen to the extremity of the penis (Fig. 21-5). In addition to the sperm tract proper, the male reproductive system includes three pairs of glands. A large seminal vesicle drains into the vas deferens on each side, near the point where the sperm duct joins the urethra (Fig. 21-5), and the prostate glands empty into the urethra. In many mammals, the prostate is plainly a double gland; but in man it ap- pears as a single mass encompassing the root of the urethra (Fig. 21-5). The prostate secre- tion enters the urethra by two sets of fine ducts that come in from either side of the mass. And finally there are Cowper's glands, a pair of glands that empty into the urethra more distally (these small glands are not shown in Figure 21-5). The composition of the semen is very com- plex. In addition to the sperm, semen con-. tains numerous glandular secretions, but the precise origin of these secetions is somewhat obscure. Probably some components of the semen are derived from the epithelium of the epididymis, and until t