Answer: Option A
:
A
A germ layer is a group of cells in an embryo, that interact with each other as the embryo develops and contribute to the formation of all organs and tissues. All animals, except sponges (sponges exhibit cellular level of organisation), form two or three germ layers. The germ layersdevelop early in embryonic life. Thus, based on the number of embryonic germ layers, organisms are categorised as diploblastic and triploblastic. Diploblastic organisms are those in which the embryonic stage includes just two layers - the ectoderm and the endoderm, from which the fully functional organism develops. A gelatinous substance called mesoglea fills the space between them. Triploblastic organisms are those which possess three germinal layers during embryonic development - the ectoderm, mesoderm and the endoderm, each of which gives rise to the various parts of the fully developed organism.