594 THE MICROSCOPE. 



muscular, to lit them to be employed as prehensile organs; 

 while on their inner they are more soft and delicate, but 

 thickly covered with rows of very minute stiff hairs, 

 directed a little backwards, and arranged closely together. 

 There are very many rows of these hairs on each of the 

 lips ; and from their being arranged in a similar direction, 

 they are easily employed by the insect in scraping or tear- 

 ing delicate surfaces. It is by means of this curious 

 structure that the busy House-fly often occasions much 

 mischief to the covers of our books, by scraping off the 

 white of egg and sugar varnish used to give them the 

 polish, leaving traces of its depredations in the soiled and 

 spotted appearance which it occasions on them. It is by 

 means of these also that it teases us in the heat of summer, 

 when it alights on the hand or face, to sip the perspiration 

 as it exudes from and is condensed upon the skin. The 

 fluid ascends the proboscis, partly by a sucking action, 

 assisted by the muscles of the lips themselves, which are 

 of a spiral form, arranged around a highly elastic, ten- 

 dinous, and ligamentous structure, with other retractile 

 additions for rapidity and facility of motion." l 



The beautiful form of the spiral structure of the tongue 

 should be viewed under a magnifying power of 250 dia- 

 meters, or a quarter-inch object-glass. 



These insects are of great service in the economy of 

 nature, their province being the consumption of decaying 

 animal matter, which is found about in quantities so small 

 as to be imperceptible to most people, and is not removable 

 by ordinary means, even in the best-kept apartments, during 

 hot weather. It was asserted by Linnaeus, that three flies 

 would consume a dead horse as quickly as a lion. This 

 was, of course, said with reference to the offspring of 

 such three flies ; and it is possible the assertion may be 

 correct, since the young begin to eat as soon as they are 

 born. A single Blow-fly has been known to produce twenty 

 thousand living Iarva3 (one of which is represented in Plate 

 VI. No. 141), and in twenty-four hours each has increased 

 its own weight above two hundred times ; in five days it 

 attains to its full size. When the larvae are of full size, 



(1) Mr. G. Newport, Cyclopccdia of Anatomy and Physiology. 



