INTRODUCTION 5 



the evidence which supports them. Paleontology is thus a limited sort 

 of zoology. 



In addition to the above features, which concern the past animals 

 themselves, the paleontologist deals also with the relation of those animals 

 to the animals of today. Whether the early beings were the' ancestors of 

 the ones now on earth, and if so, the probable lines of descent; what be- 

 came of the extinct species and what brought about their extinction; 

 what determined the succession of animals to the present time; these and 

 similar questions of an evolutionary bearing are in the domain of 

 paleontology. 



Taxonomy. — The classification of animals, with the principles on 

 which it rests, is known as taxonomy. As is pointed out later, classifica- 

 tion is based on relationship, nearly related animals being placed together 

 in the same group. This relationship is discovered from similarity of 

 structure, from facts of distribution, or from the existence of certain 

 fossils. A group in which the members are very closely related is apt to 

 be a small one. Such a group can nearly always be shown to have certain 

 similarities to one or more other groups which indicate that they are 

 related to each other. The small groups are thus combined into a larger 

 group of a higher rank, the component small groups still being distin- 

 guished from one another. A zoologist whose chief interest is the classi- 

 fication of animals is usually called a systematic zoologist. Ordinarily 

 it is possible for one person to be familiar with the minute details of 

 classification in only one group, or in a few groups, not in the whole animal 

 kingdom. One who knows the birds thoroughly may be unqualified to 

 classify reptiles or fishes. A student of insects usually knows insects of 

 all groups in a general way, but can arrange in detail the members of 

 only one order, for example, the butterflies and moths. As a rule 

 zoologists have various interests, and are called by different names. 

 The student of birds is an ornithologist; of the insects, an entomologist; 

 of the reptiles, a herpetologist. Systematic zoologists may appear to 

 have little in common; but if their work is well done, it rests in every 

 case upon the relationship believed to exist among the animals of their 

 special groups. That is, they are taxonomists. Although, as stated, 

 one person can usually master the details of classification in only a small 

 part of the animal kingdom, it is not a difficult task to learn the main 

 divisions of all the principal groups of animals,. and to be able to place 

 almost any animal at sight in its proper group. 



Evolution means the gradual or sudden change of animals through 

 successive generations. Animals of today are not like those of a few 

 million years ago, as is clearly proven by fossils. Since present-day 

 animals must have descended from ancient forms, somewhere in the inter- 

 vening generations offspring must have been unlike their parents. The 

 difference may have been small or large, and may have occurred at fre- 



