6 ELEMENTARY ANATOMY, [LESS. 



Each order consists of smaller groups, which groups bear 

 each the title family. 



Each family is composed of still smaller divisions, termed 

 genera. 



Each genus is made up of one, few or many species; each 

 species being composed of individuals differing only as re- 

 gards sex, and capable of reproducing other individuals 

 similar to themselves. 



The whole of these groups are defined by peculiarities of 

 form and structure ; that is to say, the classification is based 

 upon the number and shape of parts and organs, and not by 

 what such parts and organs do, i.e. it is morphological and not 

 physiological. 



9. One great primary group, i.e. one sub-kingdom (or 

 division) that to w r hich we belong includes, besides our- 

 selves, all beasts, birds, reptiles, frogs, toads, and efts (or 

 newts), and all fishes truly so called. The creatures of this 

 sub-kingdom agree in possessing a spine, that is a backbone 

 (or a cartilaginous or gelatinous representative of it). In all 

 the higher of these animals, including man, the backbone is 

 made up of a number of bony pieces termed vertebras, and on 

 this account the term VERTEBRATA is given to the whole 

 group, which is spoken of as the Vertebrate sub-kingdom. 



p IG- 2. A POUKPE CUTTLE-FISH FIG. 3. A CENTIPEDE, OR HUNDRED-KEGS 

 (Octopus). (Scolopendni). 



10. Another primary group, sub-kingdom, or division, in- 

 cludes all snails, slugs, cuttle-fishes, 1 and creatures of the 

 oyster and scallop class. The name MOLLUSCA* is applied to 

 this group, and the creatures composing it are often spoken 

 of as the Molluscous animals, or Mollusks. 



A third great primary group or sub-kingdom is termed 

 ANNULOSA. 3 They are creatures the bodies of which are 



1 Improperly called fishes ; as also are the oyster and its allies. 



2 Mollusca, from inottuscns, mollis, soft. 3 Annulosa, from anmthts, ring. 



