THE CLASSIFICATION OF ANIMALS. 123 



exist without interfering with perfect fertility, are said 

 to mark a variety^ or race.^ 



When several species present certain definite clia- 

 I'acters in comnaorij they are grouped as a genus ; and, 

 in the same way^ genera are grouped into larger 

 groups, and these into larger ones again, as may be 

 necessary; while, if an animal presents a character 

 quite unique, it may have not only a generic name, 

 but also a class name to itself. In other words, classi- 

 fication is made entirely according to the natural cha- 

 racters of the animals that are classed. Hence, as has 

 been said, no positive system of division into groups 

 is possible in zoological classification ; and the only 

 way to understand the classification is to master the 

 natural characters of each group by itself. 



The student should make a habit of assigning its 

 place in classification to every animal as soon as he 

 becomes acquainted with it : it is all very well to 

 know the species and variety, but these should be the 

 last things ascertained, after its general position 

 has been made clear. Let the beginner in zoology 

 call to mind all the most familiar animals ; — horse, 

 dog, cat, rabbit, rat ; sparrow, fowl, hawk, seagull ; 



' The student must note that extremes meet in the use of 

 the word " race,'' which sometimes is used to denote a sub- 

 division of a species, and sometimes is used (as a translation 

 of the word phylum) to denote one of the largest sub-divi- 

 sions of the animal kingdom. The student must also be 

 ■warned that genera and species are but too frequently 

 recorded under different names by different writers, especi- 

 ally in the earlier literature of zoology. 



