zoology: plan of study 2S 



Chapter 30, we may accept it as a useful working hypothesis, 

 which makes, as it were, a thread on which to hang the discrete 

 beads of our knowledge of particular animals. Of necessity we 

 shall describe and illustrate examples or types, but at the end 

 of each chapter shall consider the more general characters of 

 groups of animals. When we reach the rabbit we shall consider 

 physiology, and also minute anatomy, in rather more detail, 

 and those who prefer may begin with that chapter. Finally, 

 we shall discuss certain topics such as evolution and heredity 

 which concern animals in general. 



Proper consideration of the classification of animals must be 

 postponed to a later chapter (p. 706), but something must be said 

 here to explain the terms used in the following pages. Common 

 sense early recognised that animals are not all the same, but that 

 some are alike enough to each other to be included under a 

 common name. Thus all cats are recognisably cats, and are clearly 

 not dogs ; further, cats produce kittens, which in time become 

 cats, while dogs produce puppies which in turn become dogs. 

 To a set of animals distinct enough from all the rest to be called 

 by a separate name, but like enough to each other to be not 

 worth subdividing, the zoologist gives the name species. A set 

 of species with many similarities makes a genus. Genera are 

 collected into families, these into orders, these again into classes, 

 and classes into some dozen or so phyla, which comprise the 

 whole animal kingdom. Occasionally a species is so different 

 from all other species that it has to occupy a genus, a family, or 

 even a class by itself. For convenience in the handling of groups 

 with very large numbers of species, divisions such as super- 

 families and subclasses are interpolated. Families and higher 

 groups are given names which in form are always Latin plurals. 

 Every genus has a name which is a singidar Latin noun, and its 

 species are particularised by adding an adjective, also Latin, 

 which agrees in gender with its noun and is called the trivial 

 name, the two together being the specific name. All these except 

 the trivial names are written with capital initial letters, and 

 generic and trivial names are usually italicised. F'amily names 

 are usually derived by adding — idee to the root of the name of 

 one of the constituent genera. 



M.z. — 2 



