CHAPTER XI. 



OUTLINES OF CLASSIFICATION. 



IT is evident to the most superficial observer that there are 

 certain likenesses among living things in accordance with which 

 they may be arranged or classified into groups of greater or less 

 extent. These likenesses are such that a study of any member 

 of a group affords a certain amount of knowledge of all the 

 other members. If we carefully study the structure and actions 

 of a bird w r e learn a large number of facts which are true of all 

 birds, however different they may be. In like manner the study 

 of a fern, earthworm, oyster, moss, fish or oak, imparts not only 

 a special knowledge of these particular organisms, but also a 

 more general knowledge of all other plants and animals. This 

 all-important fact renders it possible to acquire a knowledge of 

 vital phenomena, in spite of the endless diversity of living things, 

 through the study of a comparatively small number of forms 

 selected as types, as will be attempted in the second part of this 

 book. Were it otherwise, the student of biology would be lost 

 in a maze of details ; and indeed a science of living things would 

 be impossible. 



A closer examination shows that larger and smaller groups 

 can be distinguished, each larger group consisting in general of a 

 number of smaller ones, and forming in its turn a single member 

 of a still larger group, and so on. 



The earthworm, for instance, is a member of a small group 

 termed a genus (Lumbricus} consisting of a number of different 

 kinds or species of earthworms (agricola^fcetidus^ etc.). .But the 

 group of earthworms (Lumbricus) is a member of a larger group 

 comprising all worms ( Vermes), and the Vermes constitute in their 

 turn a member of the still larger group Metazoa, comprising all 

 arhnals whose bodies consist of many cells. The group Metazoa 

 is in turn a member of the group of animal*, which finally forms 

 one subdivision of living things. 



