4 CLASSES OF ARTICULATED ANIMALS. 



well-known examples. In these the body is elongated 

 and composed of numerous similar segments^ each of 

 which bears at least one pair of feet ; the head, as in 

 the Insects, bears a pair of antennse, and the creatures 

 breathe air. The Spiders, whose ingenuity in wea\dng, 

 and supposed malignity, have alternately been the 

 objects of admiration and dread from time imme- 

 morial, together with the Scorpions, those terrible 

 inhabitants of tropical lands, and some other crea- 

 tm'cs, form the class of Arachnida^, in which the 

 body is never composed of more than two regions, the 

 head and thorax being completely united and bearing 

 four pairs of legs. Like the Insects, these creatures 

 also breathe air. Of the fourth class, the more pro- 

 minent members would fall, in a popular classification, 

 under that most miscellaneous denomination of Shell- 

 fish ; it includes alike the lordly Lobster and the deli- 

 cate Prawn, the humble Crab and the "fine brown 

 Shrimp," the delight of Gravesend holiday folks. 

 This group, to which the name of Crustacea^ is given, 

 is distinguished from all the rest by its adaptation to 

 an aquatic life; its members breathe by means of 

 gills, which require the constant contact of moistm-e 

 to keep them in working order. The structure of the 

 body exhibits great difierences in difierent groups of 

 Crustacea, but some of the segments of all parts of 

 the body usually bear jointed organs more or less 

 resembling legs. 



The above characters, meagre as they are, will 

 suffice to show the principal difierences between 

 Insects and the three classes of animals most nearly 

 related to them ; it will therefore be unnecessary to 

 inquire any further into the distinctive characters 

 * Gr, arachne, a spider. t Lat. crusta, a crust. 



