XX INTEODTJCTION. 



other in some trivial circumstance, while those of each group 

 agree in all their general structure. The specific name is the 

 lowest term to which we descend, if we except certain peculi- 

 arities, generally induced by some modification of native habits, 

 such as are seen in domestic animals. These are called vari- 

 eties, and seldom endure beyond the causes which occasion 

 them. 



Several genera which have certain traits in common are 

 combined to form a family. Thus, the alewives, herrings, 

 shad, &c., form a family called "CLUPEID^;, among fishes ; 

 the crows, black-birds, jays, &c., form the family COEVID^:, 

 among birds. Families are combined to form orders, and 

 orders form classes, and finally, classes are combined to form 

 the four primary divisions of the animal kingdom, namely, 

 the departments. 



For each of these groups, whether larger or smaller, we in- 

 voluntarily picture in our minds an image, made up of the 

 traits which characterize the group. This ideal image is called 

 a TYPE, a term which therewill be frequent occasion to em- 

 ploy, in our general remarks on the animal kingdom. This 

 image may correspond to some one member of the group ; 

 but it is rare that any one species embodies all our ideas of 

 the class, family, or genus to which it belongs. Thus, we 

 have a general idea of a bird ; but this idea does not corre- 

 spond to any particular bird, or any particular character of a 

 bird. It is not precisely an ostrich, an owl, a hen, or a sparrow; 

 it is not because it has wings, or feathers, or two legs ; or be- 

 cause it has the power of flight, or builds nests. Any, or all 

 of these characters would not fully represent our idea of a 

 bird ; and yet every one has a distinct ideal notion of a bird, 

 a fish, a quadruped, &c. It is common, however, to speak of 

 the animal which embodies most fully the characters of a 

 group, as the type of that group. Thus, we might perhaps 

 regard an eagle as the type of a bird, the duck as the type of 

 a swimming-bird, and the mallard as the type of a duck. 



As we must necessarily make frequent allusions to animals, 

 with reference to their systematic arrangement, it seems re- 

 quisite to give a sketch of their classification in as popular 

 terms as may be, before entering fully upon that subject, and 

 with particular reference to the diagram fronting the title- 

 page. 



