A germ layer is a layer of primitive cells that is formed by a process called gastrulation during embryogenesis.
Some animals have only one germ layer while developing e.g sponges,they are the simplest and do not have specialized tissues.
Some have two,an ectoderm and an endoderm and they are called diploblastic animals.
They have organised tissues which are co ordinated but no specialized organs e.g Cnidaria.
On the other hand all higher animals have three germ layers,ectoderm,endoderm and mesoderm therefore they are called triploblastic animals.
The cells of these three layers develop into specialized organ systems for performing different body functions in a well co ordinated way.
Each one has it’s own set of derivatives.
Following are the GERM LAYERS AND THEIR DERIVATIVES
It gives rise;
3.SENSORY epithelium of EAR,NOSE and EYE
4.EPIDERMIS including HAIR and NAILS
5.Enamel of teeth
7.Mucous glands of nose and mouth
10.Subcutaneous glands of skin
Gives rise to;
4.Inner epithelial lininng of most parts of git
Gives rise to;
1.Skeletal,cardiac and smooth muscles
2.Blood and lymph vessels
5.Bones and catilages
6.Dermis and subcutaneous layer of the skin
Also there are Neural Crest Cells,the specialized cells,of ectodermal origin which gives rise to the following structures in human body;
1.Ganglia of spinal and cranial nervs
3.Schwann and glial cells,
6.Connective tissues and bones of the fcae and skull
7.C-cells of the thyroid gland
9.Conotruncal septum in heart