CHAP, xm.] THE CAT'S PLAGE IN NATURE. 449 



(3.) Its non- arborescent external form ; 



(4.) Its incapacity for reproducing its kind by a process of budding ; 



(5.) Its habit of receiving its food into an internal cavity, and 



(6.) The more nitrogenous nature of most of its tissues. 



As to the points in which the cat resembles plants, it of course 

 agrees with them in all those characters by which it is distinguished 

 from non-living, inorganic matter. It also further agrees with all 

 plants, and also with all animals, in that at one stage of the cycle of 

 life it is represented only by a minute spheroidal mass of protoplasm 

 — the ovum or germ, 



§ 7. The cat having been thus compared with the inorganic 

 world, and with the world of plants, our next endeavour should be 

 to ascertain its position amongst animals. To be able to do this, 

 however, it is necessary to be acquainted with the mode in which 

 animals are classified ; for the number of their hinds is so prodigious 

 that it would be perfectly impossible to comprehend them without 

 the assistance of a well-arranged system of classification — a system 

 which may enable the student to conceive of different animals in masses, 

 such masses being arranged in a series of groups, successively smaller 

 and more and more subordinate. Animals, like plants, are con- 

 sidered as members of one great group, which has been fancifully 

 termed a "kingdom" — the animal kingdom containing all animals, 

 as the vegetable kingdom contains all plants. The principles adopted 

 by both zoologists and botanists in subdividing these " kingdoms " 

 are "morphological." By this term it is meant that the characters 

 upon which these classifications repose, and by which the various 

 subordinate groups are defined, are characters taken from the shape, 

 number, structure and mutual relations of the parts of which the 

 various creatures so classified are built up, and not upon what such 

 parts do — the characters refer to "structure," not to "function." 



The kingdom of animals is divided into a variety of suh-kingdoms, 

 each of which is, of course, a very large group of animals indeed. 

 Each sub-kingdom is again divided into subordinate groups termed 

 classes. Each class is again divided into orders. Each order is 

 farther subdivided into families ; each family into genera, and each 

 genus into species ; while a zoological " species " may be provision- 

 ally defined as " a group of living organisms which differ only by 

 inconstant or sexual characters." Sometimes, when a family contains 

 a great many genera which differ one from another in such a way 

 that they can be arranged in sets, then the term " sub-famil>/" is 

 given to each such set. Similarly, different sets of families may be 

 grouped together (it may be only one family in one set and the rest 

 in another), and then the term " sub-order " is employed to denote 

 each such set of families. Similarly here and there the term " sub- 

 class " may be conveniently employed for groups of orders, and 

 lastly, sets of classes may sometimes be conveniently united as a 

 province. Thus in one sub-kingdom we may merely meet with 

 classes, orders, families and genera, while in another we may meet 

 with provinces, classes, sub- classes, orders, sub- orders, families, sub- 



G G 



