This optimal temperature is ensured through the interplay of temperature receptors and cremaster muscles. When the temperature outside the scrotum is suboptimal than: the muscles under the skin of scrotum contract, drawing the testes close to the body. In contrast, when the considerable amounts of heat are generated within the body than the muscles of the scrotum loosen so that the testes hang down away from the body. In this way a fairly constant testicular temperature is maintained.
In man testes remain continuously in scrotum because he breeds continuously independent of time of year. In contrast in seasonally breeding mammals such as bats, the testes ascend through inguinal canals and remain in the body cavity during the non-breeding period. During these periods the testes undergo involution. In man the inguinal canal becomes sealed off short after birth. In whales, elephant seal, and rhinoceros the testes remain permanently in the abdominal cavity. Each testis is composed of coiled anastomosing somniferous tubules lined with epithelial cells that produce sperm cells; also interstitial cells of Leyden around the tubules produce the male sex hormone, testosterone, which promotes the development of the accessory glands and controls male secondary sex characteristics. As sperms are released into the interior of the tubules they are carried by ciliary action to the epididymis which lies on the outside of and partially encircling the testis. The epididymis is a convoluted tube of about 20 feet length and is made of a compact mass of small coiled tubules (vasa recta).
Testis and epididymis together constitute testicle. In the epididymis the sperms are stored so that they become motile. Epididymis connects with the vas deferens. Vas deferens is a muscular tube that leaves the scrotum by the inguinal canal and empties into the urethra, the duct that leads from the bladder.
The terminal portion of each vas deferens enlarges to form an ejaculatory duct, capable of contraction and expulsion of the sperms which are stored there. A glandular seminal vesicle empties into each ejaculatory duct before it connects to the urethra. The seminal vesicles secrete a viscid fluid which is expelled along with sperms. The mixture of this fluid and the sperms is known as semen. The secretions of the seminal vesicles contain glucose and fructose which are required by the sperms for their development. In the vas deferens the sperms are inactive but as soon as they mix with this secretion they become quite active. The urethra is surrounded by a prostate gland at the point where the ejaculatory ducts enter.
This gland has numerous small ducts emptying into the urethra. Thus prostate gland discharges its secretions directly into the urethra. Its secretions are thin milky in nature containing citric acid, calcium, phosphate, fibrinogenase, fibrinolysin, spermin, etc., and contribute 15—30% of the total volume of the semen. Another pair of glands, the Cowper’s glands, are also attached to the urethra about two inches below the prostate gland.
Their secretions are also alkaline and serve lubricant for the semen. The secretions of the prostate and Cowper’s glands suspend the sperms, motile them, nourish them and neutralize the normally acid environment of the urethra and of the female reproductive tract to a pH more suitable for sperm survival. Urethra communicates with the exterior of the body through a muscular structure, the penis. The penis of man is composed of three columns of spongy tissue, the corpora columns of spongy tissue, the corpora cavernosa, surrounding the urethra and a layer of skin on the outside. The tip of the penis en larees slightly to form the glens, which is normally covered by a fold of skin the prepuce. The function of penis is to deposit the semen in the aenital tract of the female.
Penis is found in all the species of mammals ii some reptiles and birds. In most reptiles and birds, one opening the cloaca serves as the passage for eggs and sperms and also for ‘the elimination of wastes and these animals mate by juxta- position of their cloaca.