WHERE ANIMALS LIVE 5 



rare in England, the heart's-ease and red clover would become 

 very rare, or wholly disappear. The number of humble bees in 

 any district depends in a great measure upon the number of 

 field mice, which destroy their combs and nests. . . . Now 

 the number of mice is largely dependent, as every one knows, 

 on the number of cats. . . . Hence it is quite creditable that 

 the presence of a feline animal in large numbers in a certain 

 district might determine, through the intervention first of mice 

 and then of bees, the frequency of certain flowers in that dis- 

 trict! ' : The influence of old maids upon the number of cats 

 was suggested by Huxley as an addition to Darwin's illustration. 



Not all of the kinds of animals that exist at the present time 

 have been studied and named. There are many forms in every 

 locality that have thus far escaped the scientist, and there are 

 vast regions of the earth's surface, both land and water, that are 

 yet to be examined. Nevertheless at least five hundred thousand 

 different kinds of animals have been described. It is obvious that 

 we can learn about only a few of this vast number. Fortunately, 

 it is possible to group these animals into large assemblages be- 

 cause of certain common characteristics; and these assemblages 

 can be subdivided into smaller groups. For example, all animals 

 with a long axis, like the human backbone, are placed in one 

 group, the vertebrates. One of the subdivisions of the back- 

 boned animals contains about eight thousand different kinds of 

 animals which possess hair and are called mammals; the mam- 

 mals may again be divided into smaller groups, one of which in- 

 cludes man. 



In this way order has been introduced into what would other- 

 wise be a very chaotic mass of isolated items of knowledge, and 

 by selecting a few members from each assemblage or subdi- 

 vision we can get a very good general idea of the entire animal 

 kingdom. This is what we propose to do in the following chap- 

 ters, and our selection will include those animals that we are most 

 likely to meet on our way to and from school or on our trips into 

 the country, and those that are of particular importance to man 



