The zygote divides repeatedly to form a multicellular structure called an embryo. A human embryo has three layers. The consequences of embryonic stage three are-
1. Consequences of ectoderm
(i) Formation of skin, sweat glands, oil glands, mammary glands etc.
(ii) Creation of hair, nails, feathers, horns, scales and scales.
(iii) Structure of retina, cornea and lens of the eye.
(iv) Covering structure of lips, lips, oral glands and tongue.
(v) Membranous labyrinth of inner ear and enamel structure of teeth.
(vi) Covering formation of pituitary gland and pineal gland.
(vii) Forms part of kidney medulla, integument of anus and cloaca.
(viii) Nervous system and sensory organs.
2. Consequences of mesoderm
(i) Formation of the dermis of the skin.
(ii) Formation of dentin of teeth and various parts of eye.
(iii) Formation of notochord, spinal cord, skeletal system, connective tissue and muscular tissue.
(iv) Formation of blood cells, lymph and lymph glands, excretory system, reproductive system and circulatory system.
(v) Structure of stomach and intestinal musculature and renal cortex.
(vi) Heart, the inner wall of the body cavity.
3. Consequences of endoderm
(i) Structure of pharynx, esophagus, stomach and intestines.
(ii) Formation of lining of digestive tract.
(iii) Formation of kidney, liver and pancreas.
(iv) Formation of middle ear and tonsils.
(v) Formation of thymus, thyroid and parathyroid.
(vi) Covering of the excretory canal, urethra and urinary bladder.
(vii) Formation of respiratory system and reproductive system.