THE GRASSHOPPER'S COUSINS
"jointed-legs"; but, since many other animals have jointed legs, the name is not distinctive, except in that the legs of the arthropods are particularly jointed, each being composed of a series of pieces that bend upon each other in different directions. A name, however, as everybody knows, does not have to mean anything, for Mr. Smith
Fig. 14. Examples of four common classes of the Arthropoda
A, a crab (Crustacea). B, a spider (Arachnida). C, a centipede (Chilopoda).
D, a fly (Insecta, or Hexapoda)
may be a carpenter, and Mr. Carpenter a smith. A phylum is divided into classes, a class into orders, an order into families, a family into genera (singular, genus), and a genus is composed of species (the singular of which is also species). Species are hard to define, but they are what we ordinarily regard as the individual kinds of animals. Species are given double names, first the genus name, and second a specific name. For example, species of a common grasshopper genus named Melanoplus are distinguished as Melanoplus atlanus, Melanoplus femur-rubrum, Melanoplus differentialis, etc.
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