INTRODUCTION. 



' N order to understand any science rightly, it needs that the student should proceed 

 J^rmM to its contemplation in an orderly manner, arranging in his mind the various 

 *-" ^11 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 misappre- 

 hension. 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 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 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 slight description will be given, and each will be considered more 

 at length in its own place. 



1st. The Vertebrates include Man and all the Mammalia, the Birds, the Eeptiles, 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 protection 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 Mollttsca, 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 Vertebrates. 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, 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. It is among these lower animals that the want of a true classification is most 

 severely felt, and the present arrangement can only be considered as provisional. 



4th. The next division, that of the Radiated animals, is so named on account of the 



