390 GILMAN A. DREW 
the inner tunic leave the cement body to invest the middle 
membrane. 
5. The space, potential or actual, between the middle tunic 
on the outside, and the inner tunic, outer membrane and middle 
membrane on the inside, is continuous throughout the sper- 
matophore. The liquid enclosed in this space serves the mechan- 
ical purpose of a lubricant and at the same time an easily flow- 
ing substance to which pressure is applied. The elastic force 
of the outer and middle tunics is transmitted through this liquid 
to the sperm mass and other structures during the act of 
ejaculation. 
6. The sperm mass extends through the aboral two-thirds 
of the spermatophore, inside the inner tunic, which is closely 
applied and united to it. 
7. The cement body is just oral to the sperm mass and at- 
tached to it by a connecting cylinder. The aboral end of the 
cement body is covered by the inner tunic, part of it at least 
by the outer membrane and possibly also by the inner mem- 
brane. If all are present, they are closely fused so they are 
hard to distinguish. The oral end of the cement body is covered 
by the inner membrane, outside of which come, in order, the 
middle membrane, outer membrane, and inner tunic. These 
are all easily distinguished from one another at this point. 
8. The middle membrane forms a tube extending from the 
position where the inner tunic and the outer membrane leave 
the cement body to the oral end of the spermatophore. Just 
beneath the cap the oral end, which, although formed as an 
open tube, is now closed, becomes closely applied to the inside 
of the cap and is spread out laterally to the ridge on the outer 
tunic to which it is firmly attached. The open aboral end 
of the tube formed by the middle membrane is plugged by 
the small oral end of the cement body which is covered by the 
inner membrane. It has no organic connection with the outer 
membrane or with any part of the cement body, except for about 
one-third of the length of the surface that is applied to the inner 
membrane where it covers the cement body (fig. 23 A, PA). The 
portion next to the open mouth of the middle membrane ad- 
