296 THE CEPHALOPODA 
but are reduced so as to be of the same width throughout (Fig. 
272, P). The fins of Ctenopteryx are similar, but are pectinated, that 
is to say, they consist of a thin membrane supported by muscular 
fibres (Fig. 259, ji). On the other hand, in species with a short and 
globular mantle the fins are shifted away from the aboral extremity, 
and are situated either in the middle of the body, as in Sepiola, 
or even near the anterior end, as in Cirrho- 
teuthis (Fig. 260). 
Except in Nautilus (Fig. 270, f) and 
Spirula (Fig. 268, pa.c), where it is shallower, 
the pallial cavity extends from its opening 
behind the head to the aboral extremity 
or summit of the body. It contains the 
branchiae and the anal, renal, and genital 
orifices (Fig. 272, Br, a, 7, g). In some 
Fic. 262. 
Internal shells of Cephalopoda. 4, shell of 
Belemnoteuthis dupiniana (Neocomian). B, shell Fig. 263. 
of Sepia Orbignyana. OC, shell of Spirulirostra The chitinous internal 
Bellardii (Miocene) ; the specimen is cut so as to shell, or gladius, of Loligo, 
show in section the chambered shell and the the anterior part upper- 
laminated ‘‘ guard” deposited upon its surface ; most. (From Lankester, 
D, shell of Spirula lwevis. (After Lankester.) after Owen.) 
forms it is divided longitudinally by a muscular junction between 
the mantle and the visceral mass, starting from either side of 
the anus: such is the case in the essentially littoral forms with 
a short pallial sac, such as Sepiola and the Octopodidae. In 
Opisthoteuthis the pallial cavity is particularly narrow and shallow, 
and the pallial sac scarcely projects ; in consequence of the diminu- 
tion of the ventral flexure the animal is flattened and discoid (Fig. 
300), and the anus has returned to the posterior position which it 
occupies in primitive Mollusca. 
Beneath the epithelium the integument contains, at least in 
