Fate of germinal layers : The embryo after gastrulation develops the three germ layers, viz., ectoderm, mesoderm and endoderm. Later a process of histogenesis starts which leads to the development of different tissues and organs.
(i) Fate of ectoderm : Following tissues, structures and organs develop from the ectoderm : Epidermis of the skin, epidermal derivatives such as
- hair and nails
- sweat glands
- conjunctiva
- cornea
- lens
- retina
- internal and external ear
- enamel of teeth
- nasal cavity
- adrenal medulla
- stomodaeum and proctodaeum
- neurohypophysis and
- entire nervous system.
(ii) Fate of mesoderm : The mesoderm forms the following derivatives:
- All types of muscles
- connective tissue
- dermis of skin
- adrenal cortex
- kidney
- circulatory system
- heart
- blood vessels
- blood
- lymphatic vessels
- middle ear and
- dentine of teeth.
(iii) Fate of endoderm : The following organs develop from the endoderm:
- Epithelium of gut from pharynx to colon
- glands of stomach and intestine
- tongue and tonsils
- lungs, trachea, bronchi, larynx, etc.
- urinary bladder, vestibule and vagina
- liver and pancreas
- adenohypophysis
- thymus, thyroid and parathyroid
- eustachian tube
- epithelium of urethra and associated glands.