Mr, Clark'j Obfervations on the Gemts Ocflrus. 301 



mod of the larva of this clafs there arc two diflmcl: plates for this 

 purpofe, one on each fide. 



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

 one of the larva of this clafs of infects in a veflbl of water; 

 when a Lubble may be extricated by preflurc, and may be distinctly 

 fern forming in the water, and on removing the preiTure the bubble 

 will be again entirely re-abforbed. 



In the larvtz of the Mufca tcnax and pendula^ in (lead of a horny 

 plate of this kind, there is provided a (lender tail of considerable 

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

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

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



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

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

 injected with the pureft mercury. They remain diftended by their 

 own inherent elafticity, and are filled with air to their minutcft ra- 

 mifications. Their appearance is fmgularly beautiful, efpecially 

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

 arifes from the air being feen through the femitranfparent, refra&ing 

 coats of the ve-fleL 



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

 than ten in number, which by diiledion 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 veffels terminate on the vifcera and ikin, in a 

 fimilar manner to the air veflels 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 firft 



fegment. See fig. 22, a. 



The 



