CEPHALOPODA. 207 
their extremities, which are enlarged and club-shaped.” The 
Paper Nautilus (fig. 112) has two of the arms webbed at their 
extremities and secreting a shell; and the Pearly Nautilus, 
alone of all living Cephalopoda, has numerous arms, more than 
ten in number, and destitute of suckers. 
The mouth leads into a cavity containing two powerful horny 
or partially calcareous jaws or mandibles, working vertically, 
very like the beak of a bird (fig. 110, mz), together with an 
‘““odontophore” or “tongue,” the hinder part of which is fur- 
nished with recurved spines. This cavity leads by a gullet, 
furnished with salivary glands, into a stomach, from which an 
intestine is continued to terminate by a distinct anus, which 
opens on the ventral surface at the base of the so-called “ fun- 
nel.” The funnel is a muscular tube placed on the under sur- 
face of the head, and communicating on the one hand with the 
external medium, and on the other with the cavity of the mantle. 
In the Vautius alone it is simply formed of two muscular lobes, 
which are in apposition, but are not united together so as to 
form a tube. In many cases there is also a special gland, known 
as the “ink-bag” (fig. 110, z), for the secretion of an inky fluid, 
which the animal discharges into the water, so as to enable it to 
escape when menaced or pursued. The duct of the ink-bag opens 
at the base of the funnel near the anus, but the Pearly Nau- 
tilus and the allied fossil forms are without this means of defence, 
which the presence of an external shell renders unnecessary. 
The respiratory organs are in the form of plume-like gills, 
placed on the sides of the body in a branchial chamber, which 
opens in front on the under surface of the body. In almost all 
the living Cephalopoda there are only two gills, one on each side, 
and hence this section is known as that of the “Dzbranchiata.” 
In the Pearly Nautilus alone there are four gills, two on each 
side, hence the name of “ Te¢vabranchiata” applied to the order 
of which this is the only living representative. In the Cuttle- 
fishes, at the base of each gill is a special contractile Cavity, 
called a “branchial heart,” by which the venous blood, returned 
from the body, is driven through the gills. In addition to these 
branchial hearts there is a true arterial heart, by which the 
aerated blood received from the gills is driven through the 
body. The admission of water to the branchiz is effected by 
the expansicn of the mantle, which allows the entrance of the 
outer water into the mantle-cavity. The mantle then contracts, 
