(i) The allantois is an extra embryonic membrane which forms a small out pocketing of embryonic tissue at the caudal end of the yolk sac.
(ii) It is the structural base for the umbilical cord that links the embryo to the placenta and ultimately it becomes part of the urinary bladder.

(i) The amnion is a double layered translucent membrane filled with the amniotic fluid.
(ii) It provides a buoyant environment to protect the developing embryo from injury, regulates the temperature of the foetus and provides a medium in which the foetus can move.

(i) Monozygotic twins - single fertilized egg splits into two embryos. The individuals are of the same sex, look alike and share the same genes.
(ii) Dizygotic twins - Two eggs are fertilized by two sperms. The two individuals may or may not be of same sex and are nonidentical.
(iii) Siamese twins - conjoined twins joined during birth.

(i) During fertilization the acrosomal membrane of the sperm releases the proteolytic enzyme called hyaluronidase to break the hyaluronic acid which .binds the follicular cells around the ovum.
(ii) This is called acrosome reaction. This helps the sperm to enter the ovum.

(i) Menopause is the phase in a women's life when ovulation and menstruation stops.
(ii) The average age of menopause is 45-50 years. It indicates the permanent cessation of the primary functions of the ovaries.

(i) Heavy and prolonged menstrual period that disrupts a woman's normal activities is referred to as menorrhagia.
(ii) Menorrhagia may be due to hormonal imbalance, ovarian dysfunction, uterine fibroids and may also be due to cancer of the ovary, uterus or cervix.

It denotes a menstrual cycle that is shorter than 21 days which may be due to hyperactivity of anterior pituitary gland, psychological disturbances, malnutrition, sexually transmitted disease etc.

(i) The Luteal phase of menstrual cycle involves formation of corpus luteum and thickening of endometrium of uterus for implantation.
(ii) The uterine wall secretes nutritious fluid for the foetus. So the phase is called secretory phase.

(i) Menstrual flow occurs due to breakdown of endometrial lining of the uterus and its blood vessels due to decline in the level of progesterone and oestrogen.
(ii) This happens when the released ovum not fertilized.

(i) It is a temporary endocrine gland formed from the ruptured Graafian follicle.
(ii) It secretes a large amount of progesterone which is essential for maintenance of the endometrium of the uterus. If fertilization does not occur it degenerates.

During the ovulatory phase of the menstrual cycle, maximum secretion of leutinising hormone occurs during the mid cycle (about 14^th day) which is called LH surge and induces ovulation.

(i) Acrosome is a small cap like pointed structure present at the tip of the nucleus and is formed mainly from the Golgi body of the spermatid.
(ii) It contains hyaluronidase, a proteolytic enzyme, popularly known as sperm lysin which helps to penetrate the ovum during fertilisation.

(i) FSH stimulates testicular growth and enhances the production of Androgen Binding protein (ABP) by the sertoli cells and helps in the process of spermiogenesis.
(ii) LH acts on the Leydig cells and stimulates the synthesis of testosterone which in turn stimulates the process of spermatogenesis.

(i) Sertoli cells are elongated and pyramidal and provide nourishment to the sperms till maturation.
(ii) They also secrete inhibin, a hormone which is involved in the negative feedback control of sperm production.

The first cleavage in zygote produces two identical cells called blastomeres. These produce 4 cells, then 8 and so on. After 72 hours of fertilization, a loose collection of cells forms a berry shaped cluster of 16 or more cells called the morula.