SUBAQUEOUS LIFE 205 



seems the arrangement whereby creatures hatched, 

 grown, and living constantly in the water cannot 

 separate dissolved oxygen for their own consump- 

 tion, as fish do, out of the surrounding medium, but, 

 like whales, must be visiting the surface perpetually 

 for a renewal of the supply. For this reason, those 

 aquatic larvse which have to pass through a motion- 

 less pupa stage mostly crawl out of the water and 

 bury themselves in moist earth to await their final 

 transformation. Certain beetles, however, have hit 

 upon devices for avoiding these constant trips to 

 the surface with all their attendant risks. Donacia 

 crassipes is equipped with two spines far back on the 

 abdomen, with a little spiracle or breathing hole at 

 the root of each. The organs of insects, be it 

 observed, have a bewildering knack of appearing in 

 those parts of the person where they are least 

 expected, and there is nothing unusually heterodox 

 in carrying nostrils on the exterior of the stomach. 

 This insect frequents the roots of water-lily and 

 other succulent aquatics, knowing that such roots 

 contain spaces filled with atmospheric air. The 

 Donacia, while feeding, probes the roots with its 

 spines, tapping the air reservoirs, and breathing in 

 their contents through the spiracles. 



