SEXUAL ACTIVITIES OF THE SQUID 383 
it may be traced to the oral end of the spermatophore, where 
it seems to end against a ridge on the inside of the outer tunic. 
The middle membrane. of the ejaculatory apparatus, to be de- 
cribed later, is firmly attached to the other side of this same 
ridge. The middle tunic is soft, evidently elastic, forming an 
elastic cushion, and is evidently capable of taking up water 
rapidly. When a spermatophore is removed from a spermat- 
ophoric sac and placed in sea-water, the middle tunic imme- 
diately begins to increase in thickness and soon the spermatophore 
begins to ejaculate, or, if the cap holds, the outer tunic is rup- 
tured by the increased internal pressure. 
If the outer tunic be cut in such a spermatophore, the sperm 
mass is driven through the opening and the middle tunic thickens 
to occupy the space formerly occupied by the sperm mass. The 
combined swelling of the middle tunic and the elastic shrinking 
of the outer tunic nearly obliterate the space formerly occupied by 
the sperm mass. Evidently these two tunics are concerned in sup- 
plying the force that causes the ejaculation of the spermatophore. 
Closely applied to the sperm mass is a very thin and not very 
definite membrane, the inner tunic (fig. 2, 77’). This is fre-° 
quently hard to identify, as it has nearly the same appearance 
as the mucilaginous material with which the sperm are mixed, 
and it is very closely applied to the mass. In the figures the 
part of the inner tunic covering the sperm mass is represented 
by a single line. 
During the formation of the spermatophore, when the ma- 
terial of this tunic is wrapped around the sperm mass, it is easily 
distinguished in sections. In spermatophores which have not 
been completely formed, before final shrinking takes place, 
the coiling of the sperm thread of the sperm mass is quite dis- 
stinct, and here the inner tunic is seen in the spaces between 
the coils of the sperm thread, separated slightly from the sperm 
mass. 
Connecting the sperm mass and the cement body is a thin 
cylinder of transparent material, the connecting cylinder (fig. 
6, CC) which seems to be a continuation of the core of the muci- 
laginous material with which the spermatozoa are mixed. The 
