In reptiles and birds, the fertilization takes inside the body and the fertilized eggs develop outside.
In mammals both the fertilization and development are internal.
Different Types
1. Female Reproductive System: The ova are produced in the ovaries, two structures attached to the body wall at the back of the abdominal cavity below the kidneys. Close to each ovary is the funnel shaped opening of the oviduct, the narrow tube down which the ova pass when they are released from the ovary. The oviducts open into a wider tube, the uterus or womb, lying lower down in the abdomen.
The lower end of uterus, usually almost completely closed by a ring of muscle called the cervix, which leads into a muscular tube called the vagina, which opens to the outside of the body. The lower opening of the vagina is called the vulva, the opening of urethra from the bladder lies close to the vulva. Graafian follicle is the region of fluid filled cavity partly enclosing the ovum and its surrounding cells. Once is every 4 weeks a Graafian follicle bursts, releasing its ovum. This is the process of ovulation and is repeated with regularity. Ovum released from this passes into the gunnel shaped opening of the oviduct. After the release of the ovum, the cells of Graafian follicle continues to grow and divide, forming a small solid structure the corpus luteum.
If the ovum is not fertilized, the corpus luteum degenerates after about 2 weeks and is gradually replaces by ordinary ovary tissue. 2. Male Reproductive System: The male reproductive cells, sperms are produced in the testes. In man the testes lies outside the abdominal cavity, suspended by the spermatic cords in a sac called scrotum. This results in the temperature of the testes being lower than the rest of the body, a condition favorable for the sperm production. The testes consist of a mass of narrow tubules {seminiferous tubules), which leads to the epididymis, a narrow tub lying in a coiled mass on the outside of the testes. It leads to a muscular sperm duct, and the two sperm ducts open into the top of the urethra just below the point where it leaves the bladder. A short coiled tube, the seminal vesicle, branches off from each sperm duct just above its opening into the urethra.
Two glands open into the urethra, the prostate gland which surrounds it at the point where it leaves the bladder, and Cowper’s gland, a little down. Urethra in males is prolonged into a penis, consisting of connective tissue containing numerous small spaces which are normally empty but are filled with blood when the penis becomes erect.