226 DIVISION II. MOLLUSCOUS ANIMALS.—CLASS II. PTEROPODS. 
Unfortunately, there is not a word of truth in this pleasing tale. Like 
the commonest cuttle-fish, the Argonaut generally creeps about at the bot- 
tom of the sea, or when he swims, he places his sails close to the shell, 
stretches his oars right out before him, and shoots backwards like most of 
his class, by expelling the water from his respiratory tube. 
As he sits loosely in his shell, he was supposed by some naturalists to be 
a parasite, enjoying the house of the murdered owner; but this is perfectly 
erroneous, as the young in the egg already show the rudiments of the future 
shell, and the full-grown animal repairs by reproduction any injury that may 
have happened to it. 
The Nautili, which likewise are provided with an external shell, are 
Cephalopods of a very peculiar kind. Tere, instead of mighty cup-bearing 
ereat number of contractile and slender 
or sharp-clawed arms, we find ag 
tentacula. The handsome pearl-mother and spirally-wound shell is divided 
by transverse partitions, perforated in the centre into a large number of 
chambers. The animal takes up its abode in the foremost and largest, but 
sends a communicating tube or siphon, the use of which is as yet but little 
known, through all the holes of the partitions to the very extremity of the 
spirally-wound shell. Recent researches in the South Sea have brought to 
light three different kinds of Nautilus: the Pompdlius, found at the New 
Hebrides and Feejee Islands; the Umbélicated Nautilus of the Solomon 
Islands, New Georgia, New Breton, and New Ireland; and 1. Macropha- 
dus, found at the Isle of Pines and New Caledonia. 
CLASS IL THE PTEROPODS. 
This class, although multitudinous in individuals, comprehends but one 
order, and a small number of species. The Pteropods ( Wing-footers) are 
thus named from their peculiar organs of locomotion, which are fins placed 
like wings at each side of the mouth. Consequently they cannot creep, and 
therefore frequent the high seas, where they swarm in countless myriads. 
They are small creatures, not exceeding an inch in length, and yet their 
numbers are so vast that they constitute the principal part of the food of 
the gigantic whale. The genera are Ci1o, which has an oblong, membranous 
body, without a cloak, and a head formed of two rounded lobes ; CyMBULIA, 
which has a cartilaginous envelope in the shape of a boat or shoe, and a 
body so transparent that we can see the heart, brain, and the viscera through 
the envelope; PNeumopERMON, which has an oval body, and furnished with 
lips, and two bundles of numerous tentacula, terminated each by a sucker ; 
Hyauea, the Hyales, have two very large wings, no tentacula, and cloak 
