Microscopical Essays. 



245 



Among the infects in which the refpiration feems to be mod 

 clearly proved, is the larva a. queue de rat (mufca pendula. Lin.) ; 

 thefe live under water in the mud, to which they affix themfelves ; 

 though they live under water, the refpiration of frefh air is neceffary 

 to their exigence ; for this purpofe they are furniOied with a tail, 

 which often appears of an exceffive length relative to their body ; the 

 body is feldom more than three quarters of an inch in length, while 

 the tail is frequently more than four inches ; it is compofed of two 

 tubes, which run one into the other, fomething fimilar to the 

 tubes of a refracting telefcope. Befides this, the materials of 

 which the tubes are compofed are capable of a great degree of 

 extenfion. When, the tail is at it's full length, it is exceeding 

 fmall, not being larger near the extremity than a horfe-hair ; 

 there is a little knob at the endj which is furnifhed with fmall 

 hairs, to extend on the water, fomething fimilar to thofe at the 

 tail of the mufca chameleon. 



In the body of the larva are two large tracheal veffels ; thefe 

 air-veflels extend from the head to the tail, and terminate in the 

 refpiring tubes, and receive the air from them. The larva quits 

 the water when the time of it's transformation approaches, and 

 enters in the earth, where the (kin hardens, and forms a cafe, in 

 which the pupa is formed ; foon after the change,, four tubes, or 

 horns, are feen projecting from the cafe : thefe M. de Reaumur 

 fuppofes to be organs for communicating air to the interior parts 

 of the infect ; they are connected with little bladders which are 

 found, filled with air, and by which it is conveyed to the fpiracula 

 of the pupa. The larva of gnats, and other fmall aquatic infects < 

 of the fame kind, are furnifhed with fmall tubes, that play on. 

 the furface of the water, and convey the air from thence to the 



