Mr. Clark'j Obfervations on the Genus Oejlrus. 301 



moft of the larva: of this clafs there arc two diAinil plates for this 

 piirpofe, one on each fide. 



That the air is admitted by thefe means, is proved by immcrfmg 

 one of the larva of this clafs of infctils in a velTcl of water; 

 when a bubble may be extricated by prcfTurc, and may be diftinclly 

 feen forming in the water, and on removing the prcflure the bubble 

 will be again entirely re-abfoibcd. 



In the larva pf the Mufca tcnax and pcndula, in (lead of a horny 

 plate of this kind, there is provided a llender tail of confiderable 

 length, with a perforated cartilaginous tube paffing through it; and 

 the extremity of this tube is elevated above the furfacc of the putrid 

 water in which they live, and conveys air to the Lirva beneath. 



On opening the body of the bot, and removing the gelatinous 

 matter, the air tubes are feen of a fplendid filvery colour, as though 

 injedled with the purefl: mercury. They remain diftendcd by their 

 own inlierent elaflicity, and are filled with air to their minuteft ra- 

 mifications. Their appearance is fingularly beautiful, efpecially 

 if the bot be alive, or recently dead. This glittering appearance 

 arifes from the air being feen through the femitranfparent,refradiniT 

 coats of the veflel. 



In this fpecies the principal trunks of the air veflels are no lefs 

 than ten in number, which by diffedlion are found to open with 

 the large ends (fee fig. 26, a) into one common refervoir beneath the 

 cartilaginous plate : this being removed with a knife, exhibits the 

 mouths of the tubes as they are arranged at fig. 24. The branches, 

 proceeding from thefe vefTels terminate on the vifcera and (kin, in a 

 fimilar manner to the air vefiTcls of the former fpecies. 



Two confiderable trunks or tubes could be traced till they termi- 

 nated in the two fmall prominent points on the edge of the firfl: 

 fegment. Sec fig. 22, a. 



The 



