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IV.-TURBOT, CoD .
VI.--SPINY-RAYED, AS THE DORY
FIRST STEPS TO ZOOLOGY.
On the titlepage of this little book is the word “Zoology." A learner will naturally ask, “What does it mean?"
It means a knowledge of animals. The science which teaches the structure, habits, and classification of animals is Zoology; the person possessed of such knowledge is a Zoologist.
When we use the word “animals” in this sense, we do not mean those only that resemble the domestic quadrupeds of these countries, or the tiger and elephant of other lands, but we include birds, fishes, snakes, and frogs. Nor do we stop with these; we apply the term to the snail and the oyster, to the crab and the worm, to the sea-urchin and the jelly-fish, and to those living atoms which the unassisted eye cannot perceive.
These creatures differ widely from each other in size, structure, and habits. Some of them are fitted to bear the cold of the arctic regions, and some to live under the scorching heat of the tropics. They people the air, the earth, and the waters, and in countless myriads are spread abroad over the entire surface of the globe.
This vast assemblage of animals it is the business of the Zoologist to distribute into groups, distinguished by some well-defined characters; so that in his classification those may be placed together which are alike, and those may be separated, more or less remotely, which are different. The task is one that no single individual could accomplish by his own efforts; but it has been effected by the combined and successive labours of many; and in this way the entire animal kingdom has been divided into four great groups. These are distinguished by their peculiarities of structure; not so much by those which are external as by those which are internal, and are connected with the nerves.
The first of the groups contains those animals which have a skull, and a backbone composed of a number of joints or vertebra, as in our own bodies. All such animals are termed "vertebrate," and all in which the skull and backbone are wanting are called "invertebrate."
The following are the four groups or sub-kingdoms established by Baron Cuvier:
I. Vertebrated animals (Vertebrata).
IV. Radiated animals (Radiata). Let us begin with those at the foot of the scale, and gradually ascend to those beings which occupy a higher rank:
“O Lord, how manifold are thy works! in wisdom hast thou made them all: the earth is full of thy riches: so is this great and wide sea, wherein are things creeping innumerable, both small and great beasts.” -PSALMS.
If we pick up a Star-fish which has been left on the beach by the retiring tide, we notice that the limbs or arms of the animal are like rays spreading out from a common centre. The Star-fish furnishes therefore a good illustration of what is meant by a "rayed” or “radiated” animal. There are, however, many others belonging to the group in which the rayed appearance is not exhibited in the outline of the body. It is easily discernible in the Sea-urchin, although the figure is rounded; but in others it must be sought for in the radiated arrangement of the parts surrounding the mouth; and in some it can only be detected by an examination of the internal structure.
The Radiated animals are arranged in four great groups or “Classes."
I. Infusory Animacules (Infusoria).