Male reproductive system
The male reproductive system consists of a scrotum, a pair of testes, vasa efferentia, a pair of epididymis, a pair of vasa deferentia, a pair of ejaculatory ducts, a urethra, a penis and certain glands.
(i) Reproductive organ
(a) Scrotum: The scrotum is a pouch of pigmented skin arising from the lower abdominal wall and hanging between the legs. Its dermis contains almost a continuous layer of smooth muscle fibres called dartos tunic. The scrotum is divided internally into right and left scrotal sacs by a muscular partition, the septum scroti. A scar like raphae marks the position of the septum externally. The testes originate in the abdominal but latter, during the seventh month of development, descend permanently into the respective scrotal sac through passages termed inguinal canal. If an inguinal canal remains open or is torn, a loop of intestine may descent in the scrotum to produce the disorder of inguinal hernia.
- A spermatic cord connects testis with abdominal cavity. It consists of connective tissue that encloses an artery, a vein, a lymph vessel, a nerve, cremaster muscle and a vas deferens. A testis rests in it chamber over pad called gubernaculum.
- Descent of testes in scrotum provides a low temperature (of\[2C{}^\text{o}\]) for maintenance of spermatogenic tissue and formation of sperms. Failure of testes to descend in scrotum is cryptorchidism, the disorder that causes sterlity because sperm formation does not occur at the abdominal temperature.
- Men persistently wearing tight underpants or taking very hot baths may have a reduced sperm count almost leading to infertility.
- The scrotal sac of male homologous to female's labia major.
Variations in position of testes: In some mammals (lion, bull, horse), the testes remain permanently in the scrotum and keep functioning throughout the year as in man. In certain seasonally breeding mammals, such as bat, otter and llama, (Insectivora, Tubulidentata, chiroptera and most Rodentia) the testes enlarge, become functional, and descent into the scrotum in the breeding season, but thereafter ascent into the abdominal cavity, and become reduced and inactive. In a few cases (elephant, whale, seal) the testes remain permanently in the abdomen as the body temperature is low enough for sperm maturation. Scrotum is absent in such cases. Scrotum is in front of penis in Kangaroo.
(b) Testes: The testes are the primary sex organs. They are about 4 - 5 cm long, 2.5 cm wide and 3 cm thick. They are suspended in the scrotal sacs by spermatic cords.
(1) Protective coats (Tunicae): Each testis has three coverings - tunica vaginalis, tunica albuginea and tunica vasculosa. On one side each testis is covered by hollowed tunica vaginalis, a bilayer of peritoneum with a narrow coelomic cavity having coelomic fluid for sliding. The actual covering
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(ii) Transverse binary fission: If the plane of cytoplasmic division concides with the transverse axis of the individual, the fission is termed transverse binary division. Example - Paramoecium and Planaria.
(iii) Longitudinal binary fission: It the plane of cytoplasmic division concides with the longitudinal axis of the individual. This kind of fission is designated as longitudinal binary fission. Example - Euglena and vorticella.
Binary fission involves mitotis only and consequently, the resultant offspring's are genetically identical to the parent and each other.
(2) Multiple fission: Multiple fission is the division of the parent into many small daughter individuals simultaneously. Examples - Multiple fission occurs in many protozoans such as Plasmodium, Amoeba and Monocytis.
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(3) Location: Each ovary is located close to the lateral walls of the pelvic cavity, being suspended from the dorsal body wall just behind the kidney, by a section of peritonium, the mesovarium. It is held in position by several connective tissue ligaments. Each ovary is connected by an ovarian ligament to the uterus, and by a suspensory ligament to the lateral pelvic wall. It has hilus where nerves and blood vessels are connected.
(4) Structure: Each ovary is a compact or solid organ, consisting of an outer cortex and inner medulla. The stroma of the cortical region is composed of spindle shaped fibroblasts. A poorly delineated dense connective tissue layer, the tunica albuginea, covers the cortex. It imparts the whitish colour to the ovary. Located outside the tunica albuginea, the germinal epithelium, formed of simple squamous or cuboidal epethelial cells, covers the surface of the ovary.
Cells of germinal epithelium give rise to groups of oogonia that project into cortex as cords called egg tubes of Pfluger, each with a round terminal mass of oogonia called egg nest. Egg nests give rise to ovarian follicles. In neonate female baby the ovary contains about 2 million follicles but 50% of them are atretic or degenerate. Atresia continues and by the time of puberty some 3,00,000 - 4,00,000 ovarian follicles are present in an ovary. However, only 450 ovarian follicloes mature, one by one alternately in the two ovaries at intervals of 28 days. A mature ovarian follicle is called Graffian follicle. It has a diameter of 10 mm. Outer fibrous theca externa and inner cellular theca internal are derived from spindle cells of cortex. Estrogen secreted by the internal theca of graffian follicle. Other constituents are follicular cells (nourishing cells formed from undifferentiated oogonia), an antrum or follicular cavity having liquor folliculi and an eccentrically placed oocyte. Follicular cells form a cellular sheath (below theca internal) called membrane granulosa and cellular mass called cumulus ovaricus covering the oocyte. Cumulus oophorus or cumulus ovaricus differentiates into outer discus proligerous and inner corona radiata. Alongwith oocyte it also secretes a mucoprotein membrane called zona pellucida. Oocyte (secondary oocyte more... 
(c) Cortical reaction: Immediately after the entry more... 
