SEXUAL ACTIVITIES OF THE SQUID 387 
The spiral filament (fig. 2, S/), while formed as a separate 
structure, evidently sticks to the inner membrane which covers 
it. The filament is brown, more or less granular, and is not of 
equal size and shape throughout. It is heaviest, with the coils 
most open, midway in its course, with both ends rather crowded. 
The loops of the spiral on the end next the cement body are 
very closely crowded, flattened, and the extreme end sometimes 
has the continuity of the thread broken so it is made up of con- 
secutive fragments. The loops of the oral end of the filament 
become closely crowded, then more open and finally fade away 
so gradually that it is hard to determine where the filament ends. 
The function of the filament is not easily determined. It is 
evidently not a coiled spring and it seems to have very little 
elastic value. It seems probable that its chief function is to 
hold the lumen of the ejaculatory apparatus freely open so that 
evagination, to be described later, can be accomplished with- 
out tearing the membranes concerned. The rapidity of the 
ejaculation must be slowed somewhat to allow time for the on- 
coming cement body and sperm mass. The resistance caused 
by breaking the spiral filament into small fragments probably 
accomplishes this purpose. 
Between the inner and the outer membranes is the middle 
membrane (fig. 2, MM). This is very transparent and fre- 
quently shows longitudinal striations, indicating the position 
of the successive windings of the sheet of which it is composed. 
It is much thicker than the other membranes and, while capable 
of much stretching, is evidently tough. It extends from the 
point where the outer membrane, together with the inner tunic, 
leaves the cement body, to the oral end of the spermatophore. 
At the aboral end, the tube formed by this membrane is closed 
by the oral end of the cement body. At the oral end this tube, 
which was open in formation (fig. 23, MM), is closed and closely 
apphed to the inside of the cap where it spreads out laterally 
and is fastened by its lateral margin to the ridge of the outer 
tunic (fig. 2, MM). In this spreading and flattening process 
the lumen of the tube is also pressed out laterally so that in form 
the end is something like a pressed-in hollow rubber ball with 
