Germ layers.

Explanation

(i)In case of multicellular animals, germ layers are formed during initial period of their embryonic development.
(ii) These germ layers further develop to form different tissues of the body.
(iii) In case of some animals, there are only two germ layers, namely ectoderm and endoderm. They are called diploblastic animals. e.g. Cnidarians.
(iv) In most of all the remaining animals, three germ layers are formed, namely ectoderm, mesoderm and endoderm, These animals are called triploblastic. e.g. Platyhelminthes onwards all.
(v)Germ layers play major role in initiation of formation of tissues and organs in the body