358 COLLECTING, REARING [CH. 



Exuviae. For external characters, at least in the Anisoptera, the exuviae 

 are perhaps preferable to the actual larvae. They are much more easily 

 collected, and much less difficult to deal with for the collection. Care must 

 be taken in removing the exuviae from the reed-stems, to prevent damage 

 to the legs. They should be prepared for the cabinet by being boiled in a 

 weak solution of caustic potash for about half-a-minute. They can then be 

 removed and thoroughly cleaned with a camel's-hair brush. When dry, the 

 exuviae may be arranged in small boxes or trays, or mounted on a transverse 

 slip of cardboard passing under the middle of the abdomen, with a little gum. 

 The pin and label may be placed at the left-hand side, if the slip be made 

 long enough (1 to 1 inches). (Fig. 186.) 



Rearing. 



According to Needham [97], the best way to rear Dragonflies is to "let 

 them rear themselves," by placing them in specially constructed cages which 

 can be sunk in the water where they live. I cannot agree with this view, because 

 (1) if the object of rearing be to get specimens, bred specimens are never 

 so good as caught ones, since they can never be properly matured, (2) if the 

 object is to study the life-history of the species, it can only be attained by 

 having the specimens constantly under observation in the laboratory. 

 Besides, very few of us live either on the edge of a lake or anywhere near a 

 suitable locality for even occasional observation of such cages. 



Obtaining the eggs. The rounded eggs of exophytic species are easily 

 obtained by catching a female while ovipositing. If the tip of her abdomen 

 be then placed in water in a small phial, she will usually continue to lay eggs in 

 large numbers. It is necessary to have the water in the phial dirty, with 

 mud, sand or small pieces of debris for the eggs to fall upon; otherwise the 

 eggs will simply all stick together, and quickly go mouldy. The elongated 

 eggs of endophytic species must be sought for in the leaves or stems of water- 

 weeds. These may be dredged ashore in masses, and then patiently examined ; 

 or, if preferred, a female may be watched while ovipositing, and the reed-stems 

 gathered when she has gone. The stems may be broken up into pieces and 

 left in water, without harming the eggs. 



In the laboratory; the eggs are best kept in flat Petri dishes, covered over 

 to prevent evaporation of the water. Decaying vegetable matter seems to 

 be essential. I have never succeeded in rearing eggs kept in pure water. 

 Rounded eggs are the more difficult to hatch. I find, however, that, even 

 if a strong growth of fungus appears on these eggs, they will usually hatch 

 if mixed with mud and debris. Rounded eggs hatch in from five days to 

 three weeks ; elongated eggs take about three weeks or a little less. 



Rearing the Larvae. The young larvae should be picked out with a 

 camel's-hair brush and segregated (a few together) in slightly deeper Petri 

 dishes, in water on which duck-weed has been floating for some time. They 

 may be fed on Paramoecium and other Infusorians. They grow fairly rapidly. 



