INSECTS. 79 



branous expansion of great delicacy and of glassy appearance, 

 supported at all points by a horny network (Fig. 69). These in- 

 sects can fly in all directions, backwards, and to the right or left, 

 as well as forwards, with equal facility. 



The substances employed as food by insects are various in 

 proportion to the extensive distribution of the class. Some de- 

 vour the leaves of vegetables, or feed upon grasses or succulent 

 plants ; others destroy timber and the bark or roots of trees ; 

 while some, more delicately organized, are content to extract the 

 juices of the expanding buds, or sip up the honied fluids from the 

 flowers. Many tribes are carnivorous in their habits, armed with 

 various weapons of destruction, and carry on a perpetual warfare 

 with their own or other species; and again, there are countless 

 swarms appointed in their various spheres to attack all dead or 

 putrefying materials, and thus aid in the removal of substances 

 which by their accumulation might prove a constant source of 

 annoyance and mischief. Such differences in their nature demand, 

 of course, corresponding diversity in the construction of the in- 

 struments employed for procuring nourishment ; and accordingly 

 we find in the structure of the mouths of these little beings in- 

 numerable modifications, adapting them to different offices jaws 

 armed with strong and penetrating hooks for seizing and securing 

 struggling prey ; sharp and powerful shears for clipping and di- 

 viding the softer parts of vegetables ; saws, files, and augers for 

 excavating and boring the harder parts of plants ; lancets for 

 piercing the skin of living animals ; siphons and sucking-tubes for 

 imbibing fluid nutriment all these, in a thousand forms, are met 

 with in the insect world, and thus provide them with the means 

 of obtaining food adapted to their habits, and even of construct- 

 ing for themselves edifices of inimitable workmanship. 



FIG. 70. PARTS OF THE MOUTH OF AN INSECT. 



The mouths of insects may be divided into two great classes, 

 those which are adapted for biting, forming what is called & per- 

 fect or vicuidibulatc mouth, and those which are so constructed 

 as only to be employed in sucking, constituting the suctorial or 

 haustettate mouth. It is in the former of these that all the parts 

 are most completely developed. The perfect mouth of an insect 



