CEPHALOPODA. 211 
furnished with suckers; by having only two gills, which are 
provided with “branchial hearts ;” by the possession of an 
“ink-bag ;” and by the fact that the “funnel” forms a complete 
tube. They are divided into two sections—Octofoda and Deca- 
poda—according as they have only eight arms (fig. 111), or eight 
arms with two additional longer processes or “tentacles” (fig. 
109). Amongst the Octofoda are the Paper Nautilus and the 
Poulpes (Octopus), The Paper Nautilus is found in the warmer 
seas of various parts of the world, generally floating at the sur- 
face. The two sexes differ, as already said, greatly in external 
appearance. The female (fig. 112) inhabits a beautiful one- 
chambered shell, which is secreted by the webbed extremities 
of two of the dorsal arms. ‘The shell is not in any way attached 
to the body of the animal, but the webbed arms are turned, 
backwards, and the animal sits in the shell with the funnel 
turned towards the keel. It swims by the jets of water emitted 
from the funnel, and crawls upon the sea-bottom, head down- 
wards, carrying its shell on its back. The male Argonaut is 
only about an inch in length, has no shell, and has all its 
arms alike, except the one which is metamorphosed into the 
“hectocotylus.” The Poulpes (Octogz) are universally distri- 
buted in the seas of both temperate and tropical regions. 
They are the “polypi” of Homer and Aristotle, and are vora- 
cious animals inhabiting rocky shores. . 
The Decapoda are chiefly found in the open sea, often in 
enormous numbers, and the best known are the Calamaries and 
Squids. The body is elongated, and is always furnished with 
lateral fins, with which they swim actively. The shell is in- 
ternal, and differs considerably in different members of the 
group. To this section of the Dzbranchiata belong the singular 
fossil forms which are known to the geologist as Belemnites. 
These singular forms are known almost solely by their com- 
plicated internal skeleton, and they appear to have abounded in 
the seas of the Secondary period. 
The second order of the Cephalopoda—that of the Zetra- 
branchiata—comprises forms characterised by being creeping 
animals, protected by an external many-chambered shell, the 
partitions between the chambers being perforated for the pas- 
sage of a membranous or calcareous tube, termed the “si- 
phuncle.” The arms are more than ten in number, and are 
devoid of suckers ; the gills are four in number, two on each side 
