INVERTEBRATE ANIMALS. 
MOLLUSCS, 
WE now come to the second great division into which all animated beings 
have been distinguished. All the creatures which we have hitherto examined, 
however different in form they may be, the ape and the eel being good 
examples of this external dissimilarity, yet agree in one point, namely, that 
they possess a spinal cord, protected by vertebra, and are therefore termed 
Vertebrated animals. 
But with the fishes ends the division of vertebrates, and we now enter upon 
another vast division in which there is no true brain and no vertebra. These 
creatures are classed together under the name of Invertebrate animals; a 
somewhat insufficient title, as it is based upon a negative and not ona positive 
principle. Whatever may be its defects, it has been too long received, and 
is too generally accepted, to be disturbed by a new phraseology, and though 
it be founded on the absence and not the presence of certain structures, it is 
concise and intelligible. 
THE first order of Invertebrate animals is called MOLLUSCA, a name 
given to these creatures on account of the soft envelope which surrounds 
their bodies. 
THE highest of the molluscs are those beinys which are classed together 
under the title of CEPHALOPODA. This term is derived from two Greek 
words, the former signifying “a head,” and the latter “a foot,” and is applied 
to these creatures because the feet, or arms as they might also be called, are 
arranged in a circular manner round the mouth. 
They are all animals of prey, and are furnished with a tremendous 
apparatus for seizure and destruction. Their long arms are furnished with 
round hollow discs, set in rows, each disc being a powerful sucker, and, when 
applied to any object, retaining its hold with wonderful tenacity. The mode 
by which the needful vacuum is made is simple in the extreme. The centre 
of the disc is filled with a soft, fleshy protuberance, which can be withdrawn 
at the pleasure of the owner. When therefore the edges of the disc are 
aprlied to an object, and the piston-like centre withdrawn, a partial vacuum 
is formed, and the disc adheres like a cupping-glass or a boy’s leather sucker. 
These discs are all under the command of the owner, which can seize any 
object with an instantaneous grasp, and relax its hold with equal celerity. 
The arms are as movable and as useful to the cuttle-fish as the 
proboscis to the elephant, for besides answering the purposes which have 
been mentioned, they are also used as legs, and enable the creature to crawl 
on the ground, the shell being then uppermost. 
Our first example is the celebrated ARGONAUT, or PAPER NAUTILUS, 
the latter title being given on account of the extreme thinness and fragility 
of the shell, which crumbles under a heedless grasp like the shell of an egg, 
and the former in allusion to the pretty fable which was formerly narrated of 
its sailing powers. It is rather remarkable, by the way, that the shell of the 
Argonaut is, during the life of its owner, elastic and yielding, almost as if it 
were made of thin horn. 
Two of the arms of the Argonaut are greatly dilated at their extremities ; 
and it was formerly asserted, and generally believed, that the creature was 
accustomed to employ these arms as sails, raising them high above the shell, 
and allowing itself to be driven over the surface by the breeze, while it 
directed its course by the remaining arms, which were suffered to hang over 
