THE ANIMAL KINGDOM. t ij 



street, number, and name, and so, by means of classifi- 

 cation, all the letters reach their destination. But all the 

 trades of each large town are classified, so that if the 

 letter had only been addressed, " Messrs. Cassell and Co., 

 Booksellers, London," we could look in that part of a large 

 book called a Directory, amongst the names of the book- 

 sellers, and there we should find the address. 



In this way all knowledge is classified, and therefore it 

 is important that before we read about individual animals, 

 we should learn how they are divided into groups ; and by 

 this means we shall-find our studies very much simplified. 



By the term Species is meant a number of animals 

 precisely alike ; as the mouse species, in which it is 

 scarcely possible to distinguish one individual from the 

 other. One may be old and another young ; one great 

 and stout, and another little and thin ; but this would be 

 no real difference. 



There may, however, be slight differences caused by 

 climate, or other circumstances which merely alter colour 

 or cause some trifling difference, without altering the 

 nature of the animal. Thus, there may be grey mice, 

 piebald mice, and white mice ; and these are called 

 varieties of the species. 



A Genus is a group embracing several species, all 

 of which resemble each other in the most important, 

 particulars, but which have certain minor differences, by 

 which they may be distinguished ; thus, the mouse is at 

 once seen to differ from the beaver or the hare by its 

 long and tapering tail, although it has teeth of the same 

 character. But there are other animals which have the 

 Same sort of tail, and are much like the domestic mouse 

 in several particulars ; and these are therefore said to 

 belong to the same genus. 



An Order is a much greater group, and includes several 

 genera. Thits, the tail may be different in every genus, 



