166 INSECTS INJURIOUS TO VEGETATION. 



own elasticity. The effect of this rapid alternate tension and re- 

 laxation is the production of a rattling sound, hke that caused by 

 a succession of quick pressures upon a slightly convex and elastic 

 piece of tin plate. Certain cavities within the body of the in- 

 sect, which may be seen on raising two large valves beneath the 

 belly, and which are separated from each other by thin partitions 

 having the transparency and brilliancy of mica or of thin and 

 highly polished glass, tend to increase the vibrations of the sounds, 

 and add greatly to their intensity. In most of our species of 

 Cicada, the drums are not visible on the outside of the body, hut 

 are covered by convex triangular pieces on each side of the first 

 ring behind the thorax, which must be cut away in order to ex- 

 pose them. On raising the large valves of the belly, however, 

 there is seen, close to each side of the body, a little opening, 

 like a pocket, in which the drum is lodged, and from which the 

 sound issues when the insect opens the valves. The hinder ex- 

 tremity of the body of the female is conical, and the under-side 

 has a longitudinal channel for the reception of the piercer, which 

 is furthermore protected by four short grooved pieces fixed in the 

 sides of the channel. The piercer itself consists of three parts 

 in close contact with each other ; namely, two outer ones grooved 

 on the inside and enlarged at the tips, which externally are beset 

 with small teeth like a saw, and a central, spear-pointed borer, 

 which plays between the other two. Thus this instrument has 

 the power and does the work both of an awl and of a double- 

 edged saw, or rather of two key-hole saws cutting opposite to 

 each other. No species of Cicada possesses the power of leap- 

 ing. The legs are rather short, and the anterior thighs are armed 

 beneath with two stout spines. 



The duration of life in winged insects is comparatively very 

 short, seldom exceeding two or three weeks in extent, and in 

 many is limited to the same number of days or hours. To in- 

 crease and multiply is their principal business in this period of 

 their existence, if not the only one, and the natural term of their 

 life ends when this is accomplished. In their previous states, 

 however, they often pass a much longer time, the length of which 

 depends, in great measure, upon the nature and abundance of their 

 food. Thus maggots, which subsist upon decaying animal or 



