Reproduction is the process by which every animal maintains the existence of its own species. It is a biological process followed by every living organisms.
Reproduction is of two types :
(A) Asexual reproduction and
(B) Sexual Reproduction.
(A) Asexual reproduction : In this process the production of animals takes place without fertilization and zygote formation. This is of following types—
(i) Binary fission : Organisms like Amoeba, Euglena, Paramecium, Vorticella, Aurelia, etc. produce by Binary fission.
(ii) Multiple fission : Plasmodium, Amoeba, Monocystis etc. produce by multiple fission.
(iii) By budding : Process of budding is followed by Sponges, Hydra, Planarians etc.
(iv) Fragmentation : This process is common in Hydra, Planarians etc.
(v) Regeneration : Sponges, Hydra, Planarians etc. produce by regeneration.
(B) Sexual reproduction : In this process fusion of two different sex gametes of same species forms zygote. This is of following types—
(i) Syngamy : This is by autogamy (Paramecium), exogamy, anisogamy and isogamy.
(ii) Conjugation : Paramecium, involving gene mixing is by conjugation.
(iii) Automixis : Paramecium reproduce by automicis.
(iv) Endomixis.
(v) Hemixis.
Partenogenesis : In parthenogene-sis ova or spem without fertilization produces the similar animals. e.g. Bee, Hydra, Wasp, protozoa etc.
REPRODUCTION IN MAN
Man is unisexual and the development of embryo takes place in the uterus of woman.
Male reproductive organs : Man has one pair of testes found suspended in the scrotal sac. From every testis a duct arises which consists of epididymis and vas deferens opens into ejaculatory duct and urethra.
Testes produce the sperms by the spermatogenesis. Sperms alongwith the secretion of prostate, Cowper’s glands and seminal vesicles form the semen.
A strip from anterior end of testes is joined with the dorsal wall of abdominal cavity.
Epididymis is the centre of sperm maturation and collection. It is about 6 metres in length. Penis is made up of spongy tissues. Its upper swollen end is called glans penis. Skin which covers glans penis is called prepuce.
Prostate gland : Its secretion is milky white and forms about 15-30% of semen. It gives odour to semen.
Cowper’s glands secrete an alkaline liquid which reduces concentration of semen.
Out of 20-40 crore sperms in ejaculated semen, only 80% are live.
Female reproductive organs : One pair of ovaries, oviducal funnels, fallopian tubes, unpaired uterus and vagina are the main female reproductive organs. The female reproductive glands are Cowper’s glands and perineal glands.
Ovaries are found attached dorsally in the abdominal cavity by the mesodermal tissue which is known as mesovarium. The oviducal funnels are attached to this tissue.
Oogenesis takes place in graafian follicles and forms one ovum and three polar bodies. In menstrual cycle the graafian follicles grow, mature and secrete the hormone estrogen and lastly the ovum is released from the follicle. In the secretory phase the formation of corpus luteum from the graafian follicles takes place which acts as an endocrine gland and secretes progesterone. The degeneration of corpus luteum marks the end of this phase. The overgrown endometrium breaks and menstruation’s initiation takes place.
The proliferative phase and secretory phase are also known as follicular and luteal phase respectively. Both phases are controlled by estrogen and progesterone hormones respectively.
Uterus : Uterus is pear shaped in structure situated in the pelvic region of abdominal cavity. Outer muscular layer of uterus wall is called myometrium and inner endometrium. Lower narrow end of uterus is called cervix. Fallopian tubes open into uterus.
In the walls of vagina bulboruethral glands are found. Their secretion lubricate vagina at the time of coitus. Above the vagina near upper end of labia minora, clitoris is found. It is homologous in structure to penis and gives excitation to woman.
In the process of intercourse sperm from semen comes in contact with ovum and fertilize it. By this process a woman gets pregnant.
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