36 Papers from the Marine Biological Laboratory. 
The outer capsule may be cut and easily slips back, so that the 
spermatophoric sac, the spermatophoric organ, and the vas deferens 
are exposed, but all are held together (as by a mesentery) by the 
wall of the capsule that joins the testis capsule. 
The inside of the wall of the spermatophoric sac is thrown into a 
large number of deep longitudinal folds, among which the spermato- 
phores lie, with their aboral ends toward the penis. As many as 79 
spermatophores have been taken from a single spermatophoric sac. 
Spermatophores of cephalopods are mentioned often by zoological 
writers, but mostly as mere references. Descriptions and figures when 
given are usually incomplete or unsatisfactory and show plainly that 
not much careful study has been made by the authors. 
Emile G. Racovitza (1894c) has given an excellent account of the 
structure and ejaculation of the spermatophore of Rossia and I have a 
rather more extended account of the spermatophores of the squid, 
Loligo, now in press (1919). 
In describing the spermatophores of Octopus comparison will be 
made to the spermatophores of Loligo described in the paper to which 
reference has just been made and the same system of lettering for the 
figures will be used. Inasmuch as the octopus spermatophore is 
simpler than that of the squid and certain structures found in the 
latter are not present in it, the reader of this paper will find certain 
peculiarities in naming. In the spermatophores of Octopus there is 
no inner tunic, and if there is an outer membrane it is so thin that it 
has not been identified. Nevertheless the terms middle tunic and 
middle membrane have been retained, although they do not occupy 
medial positions in respect to other layers. Specimens of spermato- 
phores removed from the spermatophoric sac and placed immediately 
in about 10 per cent formalin do not discharge and remain trans- 
parent and easily studied. Placing them directly into full strength 
formaldehyde does no harm, but the added strength is not needed. 
The membranes and tunics are hardened somewhat by this reagent 
and, when they are to be stained and mounted, somewhat better 
results can be had if they are not left many hours in the formalin. 
The chief difficulty is with wrinkling when the membranes are hardened, 
but this can be overcome by slow diffusion methods. 
The most successful stain for most purposes has been Ehrlich’s 
triacid. The stain may be diluted either with water or formalin 
solution, and it is usually better to use several times as much water as 
stain. The exact strength does not seem important, but with stronger 
solutions the spermatophores are stained much quicker. When 
removed from the stain the spermatophores are washed and placed 
in 10 per cent formalin for a few minutes and then mounted directly 
in glycerine jelly. If the membranes have hardened so that wrinkling 
