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, Chilognatha, is herbivorous and a common example 
is the millipede (/wlus 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. 
Crass IV.—InsEcta. 
In the Jusecta the body is sharply defined into three 
parts—the head, thorax and abdomen. The head consists of 
five segments and carries one pair of antenne@ 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 zex segments with 
no appendages. There are no true gills and respiration is 
effected by trachee. Excretion is by malpighian tubules 
and there is usually a metamorphosis. 
Insects are mainly terrestrial and rial. 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 (1) 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 /arva 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 zmago 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 edy¢ra or 
wing-covers. 
