Asexual reproduction is infrequent and includes regeneration, budding, fragmentation, and gemmule formation. Regeneration is the ability of a new individual to develop from a detached part of another individual. Regeneration also enables sponges to repair and replace damaged or severed body parts. In budding, a new individual grows out of the body of the sponge. The new developing sponge may remain attached to or separate from the body of the parent sponge. In fragmentation, new sponges develop from pieces that have fragmented from the body of the parent sponge. Sponges may also produce a specialized mass of cells with a hard outer covering (gemmule) that can be released and develop into a new sponge. Gemmules are produced under harsh environmental conditions to enable survival until conditions become favorable again.