iv] FROM WATER TO AIR 23 



CHAPTER IV 



FROM WATER TO AIR 



INSECTS as a whole are preeminently creatures 

 of the land and the air. This is shown not only by 

 the possession of wings by a vast majority of the 

 class, but by the mode of -breathing to which reference 

 has already been made (p. 2), a system of branching 

 air-tubes carrying atmospheric air with its com- 

 bustion-supporting oxygen to all the insect's tissues. 

 The air gains access to these tubes through a number 

 of paired air-holes or spiracles, arranged segmentally 

 in series. 



It is of great interest to find that, nevertheless, a 

 number of insects spend much of their time under 

 water. This is true of not a few in the perfect winged 

 state, as for example aquatic beetles and water-bugs 

 ('boatmen' and ' scorpions') which have some way 

 of protecting their spiracles when submerged, and, 

 possessing usually the power of flight, can pass on 

 occasion from pond or stream to upper air. But 

 it is advisable in connection with our present subject 

 to dwell especially on some insects that remain 

 continually under water till they are ready to undergo 

 their final moult and attain the winged state, which 



