STRUCTURE OF A WING. 319 



forth upon its complete expansion in full magni- 

 tude and beauty." 



If we were expert anatomists, and were armed 

 with a good microscope, the study of the wing of 

 a dragon-fly would prove one of great interest to 

 us. These beautiful organs, however, must be 

 examined when they are as yet but a little ex- 

 panded, as in their completely developed state 

 we should certainly fail in detecting their real 

 structure. Thin and gauze-like as they seem, 

 they are in reality double, consisting of an upper 

 and a lower surface, between which are several 

 parts which are necessary to preserve the shape 

 and carry on the functions of the wings. The 

 two surfaces of the wing enclose what are called 

 the nervures, resembling in some respects the 

 veins of a leaf. These are really fine hollow 

 tubes of some firmness, which ramify in large 

 numbers between the two membranes of the 

 wing, and thus give strength and stability of 

 figure to them. Along these tubes, or nervures, 

 branches of the air-vessels, or trachea, and of 

 the blood-vessels, run. 



From these necessary details let us turn to 

 make the difficult, but important inquiry How 



