o/‘Spirula australis, Lamarck. 13 
The ova are close-packed ; two or three may be seen on the 
same transverse line along the terminal recurrent fold of the 
oviduct. Near its termination the glandular part is developed 
(PL III. fig. 6, d). 
The membranous part of the oviduct terminates round the 
thick border of the infundibular beginning of the glandular 
part, the fine folds of which radiate therefrom. The oviducal 
gland is pyriform; its plicated substance makes a spiral turn 
before reaching the apex. 
The outlet of the oviduct (ib. fig. 1, e') is an elliptical slit, 
situated posteriorly and laterad of the valvular orifice of the 
urocardium and of the anus. 
Much loose cellular tissue connects the peritoneum with the 
long folds of the oviduct on the left side of the visceral mass. 
Spirula is almost as devoid of external organs of natation 
as Nautilus. In both the direction in which such forces act 
is retrograde. 
Nautilus exercises them mainly by virtue of the muscular 
funnel, through which it forcibly ejects into the surrounding- 
water the respiratory currents*. Spirilla superadds to this the 
ejection of that volume of water upon which the cephalic 
arms and their basal webs contract, after the fashion in which 
other Dibranchiates, especially the Octopods, propel themselves 
backwards. The dynamic of the recoil in both instances is 
exemplified by that of the cannon, when the gas of the ignited 
powder is driven into the surrounding atmosphere. Spirula 
is superior to Nautilus in the cephalic mechanism, although 
the thick cylindrical muscular sheath enclosing the buccal 
mass may exercise a similar though feebler power in the back¬ 
ward propulsion of the body ; but inferiority in the cephalic 
motor, in Nautilus , is in some degree compensated by superiority 
of the infundibular one. In both instances of multilocular 
Cephalopods the natatory power is inferior to that of existing 
Dibranchiates. 
Rumphius testifies of the “ great post-horn ” (Nautilus), “ it 
keeps itself chiefly at the bottom, creeping sometimes into the 
nets of the fishermen ; but after a storm they may be seen in 
troops floating on the water; whence one may infer that they 
congregate in troops at the bottom. This sailing, however, 
is not of long continuance ; for having taken in all their ten¬ 
tacles, they upset their boat, and so return to the bottom.” 
I have already referred to the testimony of the same obser¬ 
vant naturalist that “the little post-horn” ( Spirula ) “ hangs 
to the rocks by a thin and small door,” or disk—“ that it sets 
itself fast to the rocks.” The marginal indication of the 
* Anat. & Pliys. of Invertebrates, Bvo, 1855, p. 583. 
