246 ANNULATA. 



consists of a series of separate segments, each having one 

 (or two) pair of jointed legs Scolopendra is typical of the 

 carnivorous order of Chilopoda {Centipedes). The other 

 order, Chilogfiatha, is herbivorous and a common example 

 is the millipede {Julus terrestris). The millipedes chiefly 

 differ from centipedes by the more cylindrical body, two 

 pairs of legs in each segment and the forward position of 

 the genital aperture. 



Class IV. — Insecta. 



In the Insecta the body is sharply defined into three 

 parts — the head^ thorax and abdomen. The head consists of 

 five segments and carries one pair of antennce and three 

 pairs of jaws. The thorax has three segments and bears 

 three pairs of legs. It may also carry two pairs of wings. 

 The abdomen is jointed and has about ten segments with 

 no appendages. There are no true gills and respiration is 

 effected by tracheae. Excretion is by malpighian tubules 

 and there is usually a metamorphosis. 



Insects are mainly terrestrial and serial. The cockroach 

 is typical in all features except the absence of a meta- 

 morphosis. 



Amidst a multitude of adaptive modifications, the insects 

 conform to a remarkable extent to the general characters of 

 the class. They are divided into orders by (i) the adap- 

 tations connected with the mouth-parts or jaws, (2) the 

 condition and structure of the wings, and (3) the degree of 

 metamorphosis. 



The largest and economically the most important orders 

 are those with a full metamorphosis. The youngoneis hatched 

 as a larva which is usually more or less worm-like. The 

 larva passes through a quiescent pupal stage of varying 

 duration, and is then set free as the imago or perfect insect. 



Order I. — Coleoptera {Beetles), 



The beetles have a complete metamorphosis, the mouth 

 parts, like those of the cockroach, are of the biting type, 

 and the first pair of wings are modified into hard elytra or 

 wing-covers. 



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