no ZOOLOGY 



bered that all these differences are in some way the outcome of 

 the history of the organisms, and that the fundamental like- 

 nesses are signs of kinship, or of similar history, or both. The 

 grouping or classifying of organisms has two objects: (i) con- 

 venience, that is, to make future work easy; and (2) to express 

 the results of past study. In so far as the first motive predomi- 

 nates the classification may be artificial, that is, may bring 

 together animals that are really not closely related, though 

 possessing a superficial resemblance. The grouping together of 

 bats and birds and insects on the ground of their power of flying, 

 or whales with fishes because of their habitat, would illustrate 

 such a classification. In proportion as classification takes in 

 all the facts known with regard to animals and expresses the 

 relationship of forms classed together, it is said to be natural. 

 Every classification is in some measure artificial since we do 

 not know all the facts concerning the structure or history of 

 any organism. 



142. Terms Used in Classification. — From what has been 

 said concerning the power of multiplication in animals, the re- 

 sulting struggle for existence, the variability, and the elimination 

 of those whose variations are not suited to the various environ- 

 ments into which the offspring migrate, it will be readily under- 

 stood that even the descendants of a single pair of organ- 

 isms will come in time to be noticeably different in form, size, 

 color, and the like. The individuals of a given region will usu- 

 ally be more like each other than like their cousins who have 

 been subjected to some other kind of environment. There is 

 thus a need of terms to express the degree of difference which, 

 through these influences, finally characterizes the descendants 

 ev6n of common ancestors. Such groups of forms are usually 

 known as varieties or subspecies of the original type from which 

 they all sprang. Thus in the human race, while all men are con- 

 sidered as belonging to one common type and possibly derived 

 from the same human ancestors, there is enough difference be- 

 tween the American Indian and the Caucasian to make it neces- 

 sary to distinguish them as different varieties. Many of our 

 widely distributed animals as the dog, the horse, the common fox 

 have varieties which are readily distinguishable. 



