Internal buds or gemmules are formed by archaeocytes in mesophyl & are coated with tough spongin & spicules.
Gemmules are specialized, formed by sponges during cold or dry weather that can survive harsh conditions.
Gemmules break open when conditions improve & the cells form new sponges.
Fresh water sponges of the Spongillidae often produce gemmules prior to winter. These then develop into adult sponges beginning the following spring.