WINGS OF INSECTS. 597 



all fluid poisons are enormously increased in their power 

 for good or for evil, when injected beneath the skin ; this 

 knowledge prepares us to understand how it is that a drop 

 from the poison gland of that wonderful little fly is sum* 

 ciently potent and virulent to destroy a large animal in 

 a few minutes. Dr. Livingstone tells us that on one 

 occasion he lost forty-three oxen in as many minutes, 

 " when not more than a score of the ' Tsetse' flies could 

 be seen." The tongue is neither large nor well developed, 

 but this is in a measure balanced by the mouth and lips ; 

 the latter are muscular, and capable of affording great 

 assistance while the fly is in the act of sucking the blood 

 of its victim. The wings are long and powerful ; the legs 

 strong and muscular ; the feet provided with the usual 

 appendages, terminating in a pair of strong claws of a 

 rather large size. 



The wings of insects exhibit variety in form and struc- 

 ture, as well as beauty of colouring ; the art with which 

 they are connected to the body, the curious manner in 

 which some are folded up, the fine articulations provided 

 for this purpose, with the various ramifications by which 

 the nourishing fluids are circulated and the wings strength- 

 ened, all afford a fund of rational investigation highly 

 entertaining, and exhibiting, when examined under the 

 microscope, beautiful and wonderful design in their forma- 

 tion. Take the Libellulidce (Dragon-flies) as an example, 

 whose wings, with their horny framework, are as elegant, 

 delicate, and as transparent as gauze; often ornamented 

 with coloured spots, which, at different inclinations of the 

 sun's rays, show all the tints of the rainbow. One species 

 {Calepteryx virgo) will be seen sailing for hours over a piece 

 of water, all the while chasing, capturing, and devouring 

 the numerous insects that cross its course ; at another time 

 driving away competitors, or making its escape from an 

 enemy, without ever seeming tired or inclined to alight. 



In fine weather, female Dragon -flies are seen to deposit 

 their eggs upon the water, making a strange noise, as 

 though they were beating the water ; the cluster of eggs 

 looks like a floating bunch of small grapes. The larvae 

 when hatched, live in the water ; and it is scarcely pos- 

 sible to fancy more strangevlooking creatures. They are 



