How do sponges reproduce?

Sponges are what are referred to as hermaphrodites.  This means that they have both male and female sexual organs in one body.  Sponges have two ways of reproducing: sexual and asexual.  Sexual reproduction usually occurs when the sponge releases its male gametes into the water and this is taken in through the pores of a neighboring sponge and is taken by special cells to the eggs in order to fertilize them.  Then the fertilized eggs turn into blastulas and are generally released into the water, although there are some species in which the females keep the blastulas inside themselves for a period of development before releasing them.  These blastulas sink to the ocean floor where they attach themselves to something solid and grow.  Asexual reproduction happens by means of external buds (and occasionally by the formation of internal buds).