58 MICROSCOPIC ILLUSTRATIONS. 



upon its being immersed in that fluid, becomes a free 

 denizen of the air, incapacitated for a longer existence in 

 the former element, are of easy explanation : he would 

 tell you that the different transitions which the being has 

 to pass through, from the larva state to the condition of 

 the perfect fly, are but the semblance of a change ; for 

 that if you examine it just previous to the change, you 

 will discover the future fly folded up in the case of the 

 larva, and ready to issue forth when the covering is re- 

 moved. How badly this will serve for an explanation 

 of the whole phenomenon, and how little it detracts from 

 the greatness and the mystery of the change that has 

 been wrought, is sufficiently evident to every reflecting 

 mind : for, had the larva been examined in the early 

 state, not the slightest indications of the future fly would 

 have been traced. A gradual development of new forms 

 and new organs has been carried on under this old 

 covering, and an absorption of old forms and organs ; 

 which, however much it may seem at variance with the 

 antiquated notions of our ancestors as to there having 

 been an actual conversion of old matter into new, is not 

 a whit the less marvellous. The mere bursting forth of 

 the creature from its envelope is but a very small part of 

 the vast transaction. 



Many species of this genus of insects are, in their 

 perfect state, possessed of a sheathed proboscis, con- 

 taining instruments with which they are enabled to 

 pierce the skin of men and cattle, injecting at the same 

 time an acrimonious fluid into the wound. The species 



