INTRODUCTION. 



ZOOLOGY (zoom, animal ; logos, a discourse) treats of animals. 

 It includes every variety, from man to the tiniest micro- 

 scopic creature. Recent investigations in Comparative Anatomy 

 seem to indicate that all the varied forms of life so shade into 

 one another as to furnish no sharply-marked dividing lines : and 

 that could the animals which have become extinct be grouped 

 with those now living, the entire series from man to the animal- 

 cule would present an unbroken succession. This panoramic view 

 would give an idea of unity in the same sense as when we speak 

 of a herd of cattle, though the individuals differ in size, color, and 

 form ; or of a landscape, in which there is no break in the undu- 

 lating outline' of the far-off horizon, though it include river, 

 mountain, and valley. 



Classification. — In order to understand Zoology clearly, it 

 is necessary to separate this vast ANIMAL KING-DOM, as 

 it is called, into different groups. If we examine the general 

 structure of the various animals, and bring together those which 

 have similar peculiarities — as, for instance, a back-bone — we shall 

 form the first grand divisions, which are styled SUBKING- 

 D OMS. There are only six of these typical ideas ; each, however, 

 developed by the all-wise Creator in wonderful diversity. 



Observing the characteristics of the animals composing a sub- 

 kingdom, particularly with regard to their physiological distinc- 

 tions — as, for instance, whether they are covered with hair or 

 feathers — we reach the divisions of each subkingdom, which we 

 designate as CLASSES. 



Observing the characteristics of the individuals of each Class 

 with regard to their adaptation to their mode of life — as, for 



