CLASSIFICATION 33 



closely resemble one another. Similarly genera 

 which are somewhat alike, are again formed into 

 larger groups, and so on. The names of families, 

 orders, and classes used to be given to these 

 groups in ascending order; but it is now gener- 

 ally recognised that such names are arbitrary, 

 and that the divisions into which animals may 

 naturally be grouped are altogether irregular, 

 and not comparable with one another. Those 

 who know a little of botany will readily under- 

 stand, from their knowledge of wild flowers, that 

 natural groups cannot be arranged in a formal 

 series. 



The main branches of the animal kingdom, 

 the largest groups of all, used formerly to be 

 called sub-kingdoms. Now the main divisions are 

 often spoken of as phyla or races. Classifications, 

 although they differ much in detail, according to 

 the preferences of individual zoologists, yet agree 

 as to the main branches of the animal kingdom, 

 the chief of these are : 



1. The Protozoa, or One-celled Animals. 



2. The Ccelenterata or Two -layered Ani- 



mals. 



3. The Sponges or Porifera. 



4. The Vermes or Worms. 



5. The Arthropods or Jointed Animals, viz., 



Insects and Crustacea. 



6. The Mollusca or Shell-fish. 



7. The Brachiopoda or Lamp-She?ts. 



8. The Bryozoa or Moss-Corals. 



9. The Echinodermata or Sea-Urchins. 



10. The Chordata, including (a) tbe Hemi- 

 chordata ; (b) the Ascidians ; (c) tke Ver- 

 tebrata. 



