RESPIRATION OF INSECTS. 975 
minute tubes ; and, by the ramifications of these, even the 
minutest parts of the body are penetrated (fig. 159). These 
tubes are formed upon a similar plan with the air-vessels 
ef Plants, having a spiral fibre winding inside their outer 
membranous coat (fig. 158); by the elasticity of which 
fibre, the tube is kept from being closed by pressure. In 
this manner the air is brought into contact with almost 
Ist Pair of legs ~-~---"-- 
Ist Segment o 
thorax 
2d Pair of legs 
3d Pair of legs 
Trachez 
Stigmata 
Fig. 159.—Resrrratory Arparatus or [nsEer (NEPA). 
every portion of the tissue, and is enabled to act most ener- 
getically upon. it ; and thus the feeble circulation of these 
animals ($ 293) is in a great degree counterbalanced by 
Tr 2 
