222 DIVISION If. MOLLUSCOUS ANIMALS.—CLASS I. CEPHALOPODS. 
parts of the body, and finds its way back again to that organ, after having 
been refreshed in the lungs or branchial apparatus. The nervous system 
consists of ganglions connected by nervous filaments. From the fishes, 
the mollusks are distinguished by the absence of an internal skeleton and 
spinal marrow, and also by the great difference of their respiratory and 
locomotive organs. 
CLASS I. THE CEPHALOPODS. 
The members of this class manifest a most extraordinary structure. They 
consist of two distinct parts. The body, which, in form of a sac, opens to 
the front, encloses the branchiw and digestive organs, and the well-developed 
head, provided with a pair of sharp-sighted eyes, and crowned with a ring 
of feet, arms, or feelers. It is to this formation that the Cephalopod owes 
grow from the circumference of the 
mouth, it literally creeps upon its head. 
its scientific name; for, as the feet 
They compose but one order, which is divided into the following genera, 
according to the nature of the shell: Ocrorus, the Poulpes; Arconaura, 
the Argonauts; Lonrco, the Sleeve-fish; Serra, the Cuttle-fish ; and 
NavtTILus. 
All the Cephalopods are marine animals, and breathe through branchiwe 
rans are concealed under the mantle, in a cave or hollow, 
or gills. These org 
which alternately expands and contracts, and communicates by two openings 
with the outer world. The one in form of a slit, serves to receive the water ; 
the other, which is tubular, is used for its expulsion. 
The first four genera — and which comprises by far the great majority of 
living species — have only two sets of gills; while the last eenus, Nautilus, 
Ss} a 8 g 
which in the present epoch is only represented by a few species, has four, 
two on each side. 
According to the number of their arms or feet, — for these remarkable 
organs serve equally well for creeping or seizing prey, —the first group 
again divides into two classes, Octopods and Decapods; the former hay- 
ing only eight sessile feet, the latter ten, two of which are elongated like 
feelers. The feet are studded on the inner surface with small circular disks 
or suckers, either sessile or pedunculated. The sessile cups of the Octo- 
pods serve them as suckers, by means of which they attach themselves so 
firmly to their prey, that once seized, it cannot possibly disengage itself 
from the murderous embrace. 
The stalked cups of the Decapods cannot, indeed, serve them as suckers ; 
’ ’ 
but, to make amends for this want of adhesive powers, they are provided 
with a sharp hook fixed in the centre, and are the more formidable from 
