The house cricket spermatophore is largely protein and does not contain any chitin. It is composed of an ampulla, a handle, and a long capillary tube terminating in a pointed closure. The wall of the ampulla comprises four different layers: an outer thin layer, an evacuating fluid, a thick strong inner layer, and a transparent inner membrane. In between the inner layer and the inner membrane, at the top of the cavity, there is the pressure body, a protein mass, divided into two halves. Each half is surrounded by a thin membrane. The process of emptying a spermatophore is due to osmosis. It has been shown experimentally that the strong inner layer of the ampulla acts as a semi-permeable membrane separating two fluids of different osmotic pressure--the evacuating fluid and the pressure body. When the closure at the tip of the tube is removed, the pressure body swells, exerting a pressure on the sperm as the evacuating fluid passes inwards.