Further cell-divisions occur, and the invagination becomes deeper, until the invaginating wall nearly touches the wall which has retained its primitive position.

The dead outer layer or ectocyst lines part of the portion thus invaginated and forms the walls of a cavity within the orifice.

The function of this pouch is to form the spermatophore, which is an elastic tube formed of structureless secretion and invaginated into itself.