72 LIFE STORIES OF AUSTRALIAN INSECTS. 



CO2 is necessary for plants, which absorb it from 

 the water to build up, with other elements, in the 

 water, food to enable the plant to perform its func- 

 tions and build up tissues. Hence a circulation of 

 these necessary gases is kept up and so the water 

 in the tank is kept pure. 



We observed in one of these jars a dragon-fly 

 nymph which had just moulted, and had on its new 

 delicate-looking pale-green skin. As Ave watched, 

 another sturdy looking nymph began to stalk 

 its pale brother. It crept slowly up, having 

 little rests now and again, and finally seized its 

 victim by the middle of the back. These larvae 

 are very vr)racious, and will devour with relish' their 

 smaller brothers, the nymphs of the damsel-flies 

 and also mosquito larvcC. In collecting them 

 we once put a nymph of a large dragon-fly with 

 three may-fly larvae, and a couple of damsel-fly 

 nymphs in a test tube — a few hours later there was 

 only one living occupant of the tube — the large 

 dragon-fly nymph. In most cases, the nymphs of 

 dragon-flies usually show, to a certain degree, pro- 

 tective colouration, their colour blending with their 

 surroundings so that they can more easily seize 

 their prey ; for these creatures do not hunt and 

 chase their victims, but wait for them or slowly 

 stalk them. 



The nymphs and larvae of the larger dragon-flies 

 have a rectal chamber at the end of the abdomen 

 (Plate II, Fig. 8), the walls of which carry gills 

 which contain numerous air tubes or tracheae. Water 

 is taken into this rectal chamber, the air is abstracted 



