162 ANATOMY AND PHYSIOLOGY 



on different sides of the body generally communicate 

 with each other in the manner indicated, there are 

 riot wanting instances where such a union cannot be 

 traced. This, according to M. Leon Dufour, is the 

 case with the majority of the Hemiptera, the respi- 

 ratory arbuscles on the one side appearing quite 

 independent of those on the other. 



On examining the structure of the tracheal tubes, 

 we observe, first, an outer membrane, smooth and 

 transparent, and seemingly without fibres ; then a 

 very delicate cartilaginous filament of a pearly white 

 colour, twined spirally round, and forming a tube 

 like the windpipe of the superior animals, within 

 which there is a thin membrane adhering closely to 

 the spiral filament. The outer membrane is com- 

 monly colourless, but occasionally it is brown, red, 

 or black, and, in such cases, the ramifications of the 

 vessels can be followed more easily. The pearl- 

 loured filament, also, in recently dead specimens, 

 affords a similar advantage, as it makes the vessels 

 shine, while the air continues in them, like branches 

 of arborescent silver. 



Besides the tubular tracheae, others are occasionally 

 to be met with of an entirely different character, 

 which have received the name of vesicular air-vessels. 



anal tubes ; c, c, c, trunks closed at their extremity ; e, a blad- 

 der-like bag, receiving a branch from the longitudinal trachea ; 

 *// tracheae designed to supply the tegmina, wings, and four 

 posterior legs ; #,#, A, h 9 tracheal bags belonging to the thorax ; 

 , /;, tracheae of the anterior legs , 2, , tracheae to supply the 

 head ; m, part of the head ; o, base of the tegmina. 



