4 INTRODUCTION. 



simple, or hairy, bristly, or spiny. The commonest appendage of 

 all is perhaps one or two spines at the end of the tibiae. In leaping 

 insects the coxae and femora are sometimes greatly thickened. 



The wings are attached to the sides of the meso- and meta- 

 thorax. They are usually formed of a transparent membrane, 

 traversed by branching tubes called nervures, and may be either 

 naked, or clothed with hair or scales. The base of the fore wings 

 is usually protected above by small plates called tegulse, not 

 unlike epaulets in appearance. At the back of the mesothorax is 

 another plate called the scutellum. In many insects it is small and 

 inconspicuous, but in others it is large and conspicuous. It 

 attains its maximum of development in the Pentatomidce, belong- 

 ing to the Order Hemiptera, in some of which it is so large as to 

 cover the whole abdomen, and the wings are folded beneath it 

 when at rest. 



The limbs of insects are worked by powerful muscles, not 

 attached to a comparatively weak and jointed internal skeleton, 

 like our own, but to the tough and often rigid or horny outer 

 covering of their bodies, which is often termed an external 

 skeleton. The strength and activity of many insects are so great 

 as to be truly gigantic in comparison with that of the Vertebrata, 

 allowing for difference in size. It has been said that if an 

 elephant were as strong as a stag-beetle, it could tear up rocks and 

 level mountains ; a race-horse with the speed of a fly could fly 

 round the world like lightning ; and a man with the activity of a 

 frog-hopper could leap through the air for half a mile, or with 

 the voice of a cicada could make himself heard all over the 

 world. 



The last portion of the body of an insect is the abdomen, 

 which usually consists of from nine to eleven segments, and con- 

 tains part of the organs of digestion and respiration, and those of 

 reproduction. Of the internal anatomy of insects our space will 

 not permit us to say much. The nervous system, to which we have 

 already alluded, lies along the ventral surface of the body, instead 

 of the dorsal surface, as in Vertebrata. Along the back extends an 

 organ called the great dorsal vessel, which fulfils the functions of 

 a heart. Insects breathe by means of openings along the side of 

 the body. These openings are called spiracles, and are placed one 

 on each side of several segments of the body ; but their number 

 varies in different insects. They open into branching air-vessels 

 called tracheae. 



