22 THE WINGS. 



downwards. To describe the modifications which the 

 different parts of the legs undergo in different insects, 

 would take up a good deal of time, and it is besides 

 unnecessary, as many of them will be referred to in 

 the sequel. 



But insects are furnished with another set of loco- 

 motive organs ; they are the only articulated animals 

 that fly, and to fit them for their aerial existence, it 

 must be confessed that most of them are amply pro- 

 vided with wings. These organs, like the legs, are at- 

 tached to the thorax, but to its upper instead of its lower 

 surface ; they are usually four in number, arranged in 

 two pairs, so that only two segments of the thorax 

 can be the bearers of the agents of aerial locomotion. 

 On examination we find that the anterior segment of 

 the thorax (prothorax] has no wings, but that these 

 organs are attached on each side of the two following 

 segments (meso- and metathorax}. The wings are 

 usually membranous organs, often of extreme delicacy, 

 through which a number of branched veins, called 

 nervures, are seen to take their course. Notwith- 

 standing the delicacy of texture presented by these 

 organs, they are in reality composed of two mem- 

 branes, between which the veins above mentioned are 

 situated ; in fact, the whole membranous wing of an 

 insect may be compared to a bladder-like expansion 

 of the skin, which has become collapsed, forming a 

 double membrane everywhere continuous at the edges. 

 Of course in nature we do not meet with bladder-like 

 wings, and the two membranes are always closely 

 united together, but their structure shows that the 

 comparison given above is a just one. 



The nervures which ramify through the substance 

 of the wing in an almost infinite variety of patterns 



