XIX] 



AND BIOLOGICAL METHODS 



357 



The burner is an ordinary kerosene fount, such as is used in incubators. The 

 boards should be turned every few hours, to equalize the heating. I have 

 a series of the glorious red Lathrecista festa, taken at Cooktown in 1907, which 

 are as brilliant to-day as when I caught them. This species turns dull brown 

 if treated in any other way. Overheating (above 110 Fahr.) must be avoided, 

 since it causes an unnatural iridescence of the wings. 



The only safe way to preserve the brilliant blues of Agrionidae is to keep 

 a few specimens always in 70 per cent, alcohol, in the dark. 



LarVEG. The best method of collecting live larvae is by using a small 

 dredge-net. I use an ordinary 8 inch iron hoop, in one piece, with a strong 

 ferrule and a bag of mosquito-netting, not too deep. With a stick four or 

 five feet long, the water-weed, debris and bottom of any pond or river can 

 be easily worked, and the larvae picked out. For some localities, a straight 

 sharp edge is useful on the net, e.g. for running along a hard rocky bottom, 



Fig. 185. Dragonfly larva mounted on 

 opal glass in specimen jar containing 

 70 per cent, alcohol ( x J). Original 

 drawing by P. Tillyard. 



Fig. 186. Exuviae of Austrogomphun 



manifestus Tillyard (New South 



Wales), cleaned and mounted on a 



cardboard slip ( x 1). Original. 



or up smooth vertical rocks. Other ingenious devices are given by 

 Needham [97]. 



Larvae can be dried and carded (like Coleoptera) ; but they make better 

 specimens if kept in alcohol. The larva should be placed alive in alcohol 

 (70 per cent., or 50-60 per cent, warm to hot). As soon as it is dead, a small 

 incision should be made ventrally along segments 3-5 (mid-gut region), 

 to allow the alcohol to penetrate there. If this is not done, the contents of 

 this part of the abdomen will decay, and cause these segments to become 

 unnaturally distended, often ruining the specimen. My series of larvae are 

 mounted with silk on slips of opal glass, and placed in 4 x 1, or 4 x 1% inch 

 cylindrical specimen jars with strong bases, in 70 per cent, alcohol (fig. 185). 



