Formation of Gemmules
Throughout the formation of gemmules, masses of food - laden amoebocytes called archaeocytes feed on other cells and lay down in within them. They get surrounded by spongiocytes (other kind of amoebocytes). The latter secrete a two layered hard covering. A tiny pore, the micropyle, is left as a small opening in this protective shell. After that, some scleroblasts (spicule-producing cells) come to lie among the two layers of the shell and produce spicules. The gemmules are now finished. The parent sponge may now disintegrate leaving behind the gemmules. On revival of favorable conditions, the gemmules begin development. The centrally located archaeocytes emerge out by the micropyle as a mass which undergoes cell division and differentiation to generate a new sponge.