STRUCTURE OF WINGS OF INSECTS. 17 



increase of their numbers, they make up by their multitude for their di- 

 minutive size, the ravages committed by them are trifling- and insignificant. 

 Far otherwise, however, would it be, if they attained to larger growth, and 

 still possessed the extraordinary power with which they are now so con- 

 spicuously gifted; they would then, indeed, become truly the tyrants of crea- 

 tion, monsters such * as fables never feigned, nor fear conceived,' fully 

 adequate to destroy and exterminate from the surface of the earth all that it 

 contains of vegetable or of animal life. 



" The flea or grasshopper will spring two hundred times its own length ; 

 the dragon-fly possesses such indomitable strength of wing, that for a day 

 together it will sustain itself in the air, and fly with equal facility and 

 swiftness backwards or forwards, to the right or to the left without turning; 

 the beetles are encased in a dense and hard integument, impervious to or- 

 dinary violence ; and we might add, that the wasp and the termite ant will 

 penetrate with their jaws the hardest wood. Neither is the velocity of the 

 movements of insects inferior to their prodigious muscular power. 'An 

 anonymous writer in Nicholson's Journal,' say Kirby and Spence, ' calcu- 

 lates that in its ordinary flight the common house-fly (Masca domestica) 

 makes with its wings about six hundred strokes, which carry it five feet, 

 every second ; but if alarmed, lie states their velocity can be increased six 

 or seven fold, or to thirty or thirty-five feet in the same period. In this 

 space of time a race-horse could clear only ninety feet, which is at the rate 

 of more than a mile in a minute. Our little fly, in her swiftest flight, will 

 in the same space of time go more than the third of a mile. Now, compare 

 the infinite difference of the size of the two animals (ten millions of the 

 fly would hardly counterpoise one racer), and how wonderful will the 

 velocity of this minute creature appear ! Did the fly equal the race-horse 

 in size, and retain its present powers in the ratio of its magnitude, it would 

 traverse the globe with the rapidity of lightning.' " T. Rymer Jones. 



27. The wings are dry, membranous, elastic appendages, usu- 

 ally diaphanous, attached to the sides of the back of the thorax. 

 They are composed of two thin membranes, laid one on the other, 

 joined together by horny lines called nervures, which are in fact 

 so many tracheal tubes for the passage of a r. 



28. The wings of insects differ much in texture : in place of 

 being membranous and transparent, as in flies and bees, they are 

 sometimes opaque and covered by a multitude of little scales like 

 dust, as in butterflies ; and at other times we observe them acquire 

 a thickness and consistence so great that they resemble horn, 

 and do not differ from other hard parts of the insect, as in the 

 may-bug, for example. It is only the first pair of wings that 

 present this latter condition ; when thus modified they are not 

 suitable for flight, but form a species of shield for the protection 

 of the upper part of the body, and are named elytra. Sometimes 

 the elytra, instead of being horny throughout their whole extent, 

 are membranous towards the end, as in wood-bugs: they are 

 then called demi-elytra. 



27. What are wings ? What are nervures ? 



28. In what respects do wings differ from each other ? What are ely- 

 tra ? What are demi-elytra. 



2* 



