78 ANIMAL ACTIVITIES. 
Breathing of a Dragon-fly Nymph. An insect 
living in the water must breathe, and it is interesting 
to observe how insects which have chosen an aquatic 
life have adapted their breathing-organs to the medium 
in which they live. The dragon-fly larva does not 
trouble himself to come to the surface for air, but 
simply takes his oxygen from the air dissolved in the 
water. The spiracles which would allow water as well 
as air to enter the breathing-tubes are closed and covered 
by the hard exo-skeleton, but the trachez or breath- 
Fic. 69.—The Imago of a Dragon-fly. 
ing-tubes, like those in the grasshopper, convey the 
air throughout the body. To get the air, the water is 
drawn in through the anal opening, where it comes in 
contact with some modified air-passages which have 
somewhat the function of gills. In these air-passages 
the carbon dioxide and other impurities await the 
opportunity to pass by osmosis to the water, while the 
oxygen penetrates through the membranes into the 
breathing-tubes. If a fine stream of bright-colored 
liquid be put near a nymph by means of a small 
pipette the currents produced by the breathing may be 
seen. 
