ORGANS FOR BREATHING IN WATER-GRUBS. 159 



but consisting only of two tul)cs, tlie outer one serv- 

 ing as a slioatli, within wliicli the inner one can be 

 retracted at pleasure. Jioth of these are composed of 

 fibrous rings; and are so very extensile, that R' aumur 

 has seen them pushed out to twelve times the length 

 of the body of the maggot. The contrivance by which 

 the inner tuhe is pushed out is no less simple than 

 ingenious. It is lurnishcd at the hase with two 

 flexihic pipes, coiled up, when it is sheathed, into 

 several lolds and communicating with the douhlc 

 wind-pipe ( Travlua) in the hody. When it wishes 

 to extend this breathing-tube, therefore, it inflates, by 

 means of air from the wind-pipe, the tlexihle pipes, 

 and in this way pushes them outward, and with them 

 the breathing-tube, to the extent required. The 

 breathing-tube itself is very slender, but terminates 

 similarly to those of the grub of the chameleon fly, in 

 five bristles. This breathing apparatus is admirably 

 adapted to the economy of these maggots ; as from 

 their seeking their food amongst ooze and mud, they 

 would otlen be exjwscd to suffocation, which their 

 extensile tube efiectually prevents. 



Water worms fiVaw J. a a a, hali-concoHled in the sand. 

 6 6 6, their sand-tubes exposed. 



