: INTRODUCTION. 
In order to understand any science rightly, it needs that the student should 
proceed to its contemplation in an orderly manner, arranging in his mind the 
various portions of which it is composed, and endeavouring, as far as possible, 
to follow that classification which best accords with nature. The result of 
any infringement of this rule is always a confusion of ideas, which is sure to 
lead to misapprehension. So, in the study of living beings, it is necessary to 
adhere to some determinate order, or the mind becomes bewildered among 
the countless myriads of living creatures that fill earth, air, and water. 
As a general arranges his army into its greater divisions, and each division 
into regiments and companies, so does the naturalist separate the host of living 
beings into greater and smaller groups. The present state of zoological 
science gives five as the number of divisions of which the animal kingdom 
is composed. These are called Vertebrates, Molluscs, Articulates, Radiates, 
and Protozoa. Of each of these divisions a slight description will be given, 
and each will be considered more at length in its own place. 
ist. The VERTEBRATES include Man and all the Mammalia, the Birds, the 
Reptiles, and the Fish. 
The term Vertebrate is applied to them because they are furmshed with a 
succession of bones called “ vertebre,” running along the body and forming 
a support and protection to the nervous cord that connects the body with the 
brain by means of numerous branches. 
2nd. The MOLLUusCaA, or soft-bodied animals, include the Cuttle-fish, the 
Snails, Slugs, Mussels, &c. Some of them pessess shells, while others are 
entirely destitute of such defence. Their nervous system is arranged on a 
different plan from that of the Vertebrates. They have no definite brain, 
and no real spinal cord, but their nerves issue from certain masses of nervous 
substance technically called ganglia. 
3rd. The ARTICULATES, or jointed animals, form an enormously large 
division, comprising the Crustaceans, such as the Crabs and Lobsters, the 
Insects, Spiders, Worms, and very many creatures so different from each 
other, that it is scarcely possible to find any common characteristics. 
4th. The next division, that of the RADIATED animals, is so named on 
account of the radiated or star-like form of the body, so well exhibited in the 
Star-fishes and the Sea-anemones. 
5th. The PROTOZOA, or primitive animals, are, as far as we know, devoid 
of internal organs or external lin bs, and in many of them the signs of life 
are so feeble, that they can scarcely be distinguished from vegetable germs. 
B 
