STRUCTURE OP CEPHALOPODS AND PTEROPODS. 117 
the fin-like tail. By which the animal is propelled through the 
water very much in the manner of a fish. The Pearly 
Nautilus is the only type now existing of an inferior order of 
Fig. 57.— Calamary. 
Cephalopods, which approaches the Gasteropods in many parts 
of its organization. The "body is inclosed in the last chamber 
of a shell (usually spiral in form), 
the cavity of which is divided by 
numerous transverse partitions ; and 
such shells, the fossilized remains of 
very numerous forms of this group 
that existed in the ancient seas, con¬ 
stitute the nautilites , ammonites, 
belemnites , &c., which abound in 
. many rocks (fig. 58). The Cuttle¬ 
fish are animals of considerable 
activity; their mouth is furnished 
with a horny beak, strongly resem¬ 
bling that of the parrot; and their arms are provided with 
a series of very curiously constructed suckers, by the action 
of which they can take a very firm 
hold of anything which they desire 
to grasp. 
112. The class of Pteropoda, or 
wing-footed Mollusks, consists of 
but few species, and the animals 
which it contains are all of them of 
small size ; but the individuals are 
often very numerous, whole fleets 
of them being sometimes seen 
covering the ocean, especially in 
the Arctic and Antarctic regions, 
where they constitute one of the 
principal articles of food to the Whale. The general form of the 
body usually differs but little from that represented in fig. 59 . 
Fig. 59.— Hyal-ea. 
