CEPHALOPODS. 
3 2 7 
a 
UPPER («) AND LOWER (b) PORTIONS OF THE 
BEAK OF A CUTTLE-FISH (Sepia). 
equivalent of the shell of the nautilus, or of the gastropods. It is not attached 
to the animal by any special muscle, but held to the body by two of the arms, 
especially developed for this purpose. It is, in fact, merely a receptacle for the 
ova, but at the same time affords protection to the argonaut herself. All the rest 
of the octopods are without shells of any description. 
The body of a cephalopod consists of a muscular sac, in the cavity of which 
the viscera are placed. In front of the body projects the head, which, in one of 
the two main sections into which the class has been divided—namely, the 
Dibranchiata, or those provided with only one pair of gills—is crowned with eight 
or ten fleshy muscular arms, in the midst of which the mouth is situated. This is 
armed with two strong jaws, in shape very similar 
to the beak of a parrot. They are curved, 
pointed, and of a horny substance in the two- 
gilled cephalopods, and somewhat calcareous in 
the four-gillecl group. Within the mouth is the 
rasping tongue, covered with the sharp siliceous 
hook-like cusps or teeth, arranged in regular 
transverse series, one behind the other. The 
eyes, two in number, are placed on each side of the head, and are of enormous size 
in some of the decapods. On the ventral side the muscular sac is disconnected with 
the head, leaving a more or less wide opening admitting the water to the gills. The 
water is then expelled through the so-called funnel with more or less force, according 
to the requirements of the animal. If it be at rest, the expulsion of water is carried 
on very quietly, but, on the contrary, with much greater force if the animal is in 
motion. Besides water, other secretions from the body are extruded through the 
funnel, and especially a dark fluid secreted in a special ink-pouch. When disturbed 
or irritated, this ink is discharged by all cephalopods, excepting the nautilus, and is 
supposed to be a means of defence. Mixing with and clouding the surrounding 
water, we can well suppose that the attack of a pursuing fish might be checked, and 
the squid or cuttle effect its escape in the darkened fluid. The arms, or feet, of the 
octopods and decapods are more or less elongate and capable of movement in any 
direction, and are furnished on one side with numerous suckers, by means of which 
the animal holds on to anything that it may seize with such tenacity that the suckers 
themselves are liable to be torn away rather than loose their hold. They are often 
furnished at the edge with a toothed horny or calcareous ring, and connected with 
the arms by slender stalks. Cephalopods employ their arms in walking and 
climbing, and, owing to their position, have to progress head downwards when 
creeping on the sea-bottom. They are connected at the base by a skin, in some 
species extending some distance up the arms, and forming a sort of umbrella, which 
is doubtless of use in the capture of their prey. In the nautilus the arms are 
different, being short, pointed tentacles, unprovided with suckers. 
The nervous system is more developed than that of other molluscs; it is con¬ 
centrated around the gullet, and protected by a cartilaginous plate, a sort of rudi¬ 
mentary skull. The skin of the naked cephalopods is more or less thickly studded 
with points or dots of various colours. These pigment-cells are subject to alter their 
tint at the will of the animal, which, chameleon-like, assumes very different aspects. 
