Cells then migrate around the helpless prey and digestion takes place extracellularly. Most poriferans that reproduce by sexual means are hermaphroditic and produce eggs and sperm at different times. That is, sperm are created, concentrated and sent out the excurrent openings, sometimes in masses so dense that the sponges appear to be smoking. These sperm are subsequently captured by female sponges of the same species. Inside the female, the sperm are transported to eggs by special cells called archaeocytes .
Fertilization occurs in the mesenchyme and the zygotes develop into ciliated larvae.
Some sponges release their larvae, where others retain them for some time. Once the larvae are in the water column they settle and develop into juvenile sponges. Sponges that reproduce asexually produce buds or, more often, gemmules, which are packets of several cells of various types inside a protective covering. Fresh water sponges of the Spongillidae often produce gemmules prior to winter. These then develop into adult sponges beginning the following spring.