SEXUAL ACTIVITIES OF THE SQUID 389 
5. The region just aboral to the cap: 1, Outer tunic; 2, 
middle tunic; 3, space (actual) filled with liquid; 4, middle mem- 
brane (the inner tunic and outer membranes do not extend 
this far); 5, inner membrane; 6, lumen (the spiral filament does 
not extend this far). 
If each structure is considered in turn in their longitudinal 
relations we find: 
1. The outer tunic is continuous over the whole spermato- 
phore except at the oral end where there is a modification, the 
cap, which is spirally wound around the otherwise open tunic 
to form a closing mechanism. ‘The cap has attached to it a 
long thread which, when pulled, serves to loosen the cap and thus 
liberate the enclosed mechanisms. 
2. The middle tunic is continuous throughout the length of the 
spermatophore up to the thickened ridge on the outer tunic 
near the oral end, which it joins. . 
3. The inner tunic is continuous over the region of the sperm 
mass as a closely investing, thin membrane. It becomes thicker 
over the posterior end of the cement body. After leaving the 
cement body as an investing membrane it becomes a little thicker 
and closely covers the outer membrane. Near the region of 
the anterior extremity of the spiral filament this tunie ends with 
open mouth closely associated with the outer membrane. 
4. The outer membrane probably begins at the aboral end 
of the cement body, but cannot be definitely distinguished from 
the inner tunic until near the place where both of these struc- 
tures leave the cement body and, together, give the appearance 
of a double membrane. After leaving the cement body the 
outer membrane is applied to the middle membrane. A short dis- 
tance orally from the end of the inner tunic the outer membrane 
also ends with an open mouth. It is important to understand 
that the oral portions of the inner tunic and the outer membrane 
together forma tube, closed at the aboral end where they are 
united to the cement body, and open at the oral end. The 
opening is of course closed by the other structures. There is, 
however, no organic union between these structures and the 
other membranes from the point where the outer membrane and 
