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 endeavoring, 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 mindbecomes 

 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 connection 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 auspi- 

 cious 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 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 furnished with a succession 

 of bones called " vertebrae," running along the body and forming a support and protec- 

 tion to the nervous 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 MOLLUSCA, or soft-bodied animals, include the Cuttle-fish, the Snails, Slugs, 

 Mussels, etc. 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 



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