NT eet C0 tO) N, 
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. 
That some determinate order exists is evident to any thinking mind, but the 
discovery of the principle on which this order is founded is a problem that as yet has 
received but a partial solution. We already know some of the links of that wondrous 
chain that connects Man with the microscopic animalcule, but the one plan on which the 
Animal Kingdom is formed, has yet to be made known. 
It is impossible to contemplate the vast mass of animal life without the conviction 
that the most supreme harmony has been observed in their creation, and the most perfect 
order exists in their connexion one with the other. Whatever may be the key to this 
enigma,—and it is of a certainty a very simple one, possibly eluding us from its very 
simplicity—from the days of Aristotle to the present time zoologists have been diligently 
seeking for the true system of animated nature; and until that auspicious discovery be 
achieved, we must be content with making as near an approximation as possible. 
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, the highest of which is 
that in which Man himself is, by some, placed. These are called Vertebrates, Molluscs, 
Articulates, Radiates, and Protozoa. Of each of these divisions a slhght 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 furnished with a succession of 
bones called “vertebre,” running along the body and forming a support and protection to 
the neryous cord that connects the body with the brain by means of numerous branches 
The Vertebrates, with one or two known exceptions, have red blood and a muscular 
heart. 
2d. The Mo.uusca, or soft-bodied animals, include the Cuttle-fish, the Snails, Slugs, 
Mussels, &c. Some of them possess shells, while others are entirely destitute of such 
defence. Their nervous system is arranged on a different plan from that of the Verte- 
brates. They have no definite brain, and no real spinal cord, but their nerves issue from 
certain masses of nervous substance technically called ganglia. 
3d. The ARTICULATES, or jointed animals, form an enormously large division, com- 
prising 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 
B 
