38 Papers from the Marine Biological Laboratory. 
the cut rapidly. The turgidity, as in the case of the squid spermato- 
phore, is due to the tough elastic and stretched outer tunic. 
The outer tunic (figs. 1 and 5 or) is thin and nearly transparent, 
although faintly amber in color. It is not as colorless as that of the 
squid and is much thinner. Magnified as shown in figure 1, it is so 
thin that it is represented by a single line. The fact that, although 
the spermatophore of Octopus is much larger than that of the squid, 
the outer tunic is actually thinner, accounts for the difference in 
turgidity and that in ejaculation Octopus spermatophores are much 
slower than those of the squid. 
The outer tunic forms the covering for the spermatophore to the 
oral extremity. The oral end is covered by the cap (figs. 1 and 2c), 
which is thinner than the outer tunic, more transparent, and is evi- 
dently more affected by water. 
Over the cap is thrown a broad cap-thread (cr) that adheres rather 
strongly to one side of the spermatophore and extends aborally for a 
distance considerably greater than the length of the ejaculatory 
apparatus. The other end of the cap thread seems always to be free 
from the spermatophore, but is folded well over the extremity of the 
cap, frequently back to the end of the ejaculatory apparatus, as a 
broad, striated bandage. 
Pulling the cap thread seems to start ejaculation of the fresh sper- 
matophore. How it is used to start normal ejaculation is not known, 
but it seems probable that the thread is pulled in some way. The 
spermatophore leaves the penis aboral end first and it seems reasonable 
to suppose it reverses ends when started down the groove of the hec- 
tocotylized arm. It is not known how it reaches this groove, but the 
groove has no connection with the penis and it seems probable that 
the spermatophore must pass through the funnel in being transferred 
to the groove. The mechanics of the transfer is not known, but it is 
probable that the thread is pulled during the process. A spermato- 
phore placed in sea-water will usually ejaculate rather promptly even 
when the cap thread is not pulled intentionally. This may be due 
entirely to osmotic changes and dissolving effects of the water or it 
may be that the thread is always disturbed enough by removal from 
the spermatophoric sac to weaken the cap end. 
Inside the aboral portion of the outer tunic, corresponding pretty 
closely with the length of the sperm mass, is a closely adhering mem- 
brane, the middle tunic (fig. 1 mr). This is not nearly as thick and 
conspicuous as the middle tunic of the spermatophore of the squid 
and does not show a granular structure. It does not line the extreme 
aboral end of the outer tunic and gradually thins out and disappears 
just beyond the oral end of the sperm mass. 
The middle tunic evidently swells rapidly in water, but it does not 
have as great osmotic properties as the middle tunic of the spermato- 
