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ILLUSTRATED NATURAL HISTORY. 
CUTTLE-FISH : DIVISION MOLL0SCA. 
Some of the lower forms, arranged with the moHuscous animals by modern zoologists, possess 
only a single ganglion, from which filaments are given off in all directions ; and between this and 
the highly complicated structure, we meet with every conceivable gradation. 
As might be expected from the great differences displayed by the members of this division 
of the animal kingdom, in regard to the degree of development of the nervous system, the 
senses are possessed by them in very various degrees of perfection. In some of the lowest forms 
the universal sense of touch appears to be the only one present ; but as we ascend in the scale, we 
meet with creatures more highly endowed in this respect. Tentacles, or special organs of touch, 
frequently occur, generally in the neighborhood of the head ; organs of sight, hearing, smell, and 
taste make their appearance, until in the highest forms of molluscous animals we find the organs 
of the senses as fully developed as in many of those belonging to the highest division. 
The skin of these animals generally lies loosely about the body, so as to form a sort of cloak or 
mantle. The mantle frequently possesses the power of secreting a hard substance, well known as 
the shell, which serves for the protection of the creature. It increases with the growth of the ani- 
mal, and varies in form according to the species which inhabits it. 
The intestinal canal is very variable in its structure, but always presents two openings — a mouth 
and an anus ; the liver frequently attains a very great degree of development. 
The circulatory system is generally very highly organized ; a heart, often divided into several 
compartments, with arteries and veins penetrating all parts of the body, existing in nearly all the 
MoUusca. The blood is colorless, or nearly so. 
The Mollusca are oviparous animals ; the male and female organs are frequently in separate in- 
dividuals, although many species are hermaphrodite. 
In the fifth and highest division of the animal kingdom, we meet with a series of organs to 
which nothing similar occurs in the groups which have already passed under review. 
All these animals possess a nervous system, consisting essentially of a brain, inclosed within a 
bony case, the skull, beneath which the oesophagus passes, and a single cord of nervous matter, 
