Dragon-flies and Damsel-flies 85 



as the weather permits, and continuing industriously to the close of the 

 season. 



The nymphs cast the skin repeatedly during their growth and develop- 

 ment, although the exact number of moultings is not known for any species. 

 After two or three moults the wing-pads appear and with each successive 

 moult increase in size. Immediately after moulting the nymphs are light 

 greenish or gray, and their characteristic color pattern is distinct, but they 

 gradua'ly darken, the pattern becoming more and more obscure until by 

 the t me for another moulting the body is uniformly dark and dingy. The 

 nymphs (Fig. 115) of the damsel-flies are elongate and slender, and have 

 three long conspicuous gill-plates at the tip of the abdomen, which they 

 can also use as sculls for swimming. The dragon-fly nymphs are robust- 

 bodied, some of them indeed having the abdomen nearly as wide as long 

 and much flattened. All the nymphs are provided with the long grasping 

 lower lip, which can be folded mask-like over the face when not engaged 

 in seizing prey. The mandibles are strong and sharp and the whole mouth 

 is well fitted for its deplorable but necessary business. 



The true dragon-fly nymphs do not have plate-like gills, like those of the 

 damsel-flies, nor any other external kind, but have the posterior third of 

 the intestine lined with so-called internal gills. These internal or rectal 

 gills are in six longitudinal bands, each consisting of two thin rows of small 

 plates or tufts of short slender papillae. Water is taken into the intestine 

 through its posterior opening and, after bathing the gills, giving up its dis- 

 solved oxygen, and taking up carbon dioxide, it is ejected through the same 

 opening. When this water is ejected violently it serves to propel the nymph 

 forward. It is also apparently occasionally used for defence. 



Just as the adult flying dragon-flies keep to certain regions above or 

 in the neighborhood of the pond, so Needham has found the nymphs to 

 have various preferred lurking-places in the pond. The damsel-fly nymphs 

 and a few of the more active dragon-fly nymphs clamber among submerged 

 vegetation or inhabit driftwood and submerged roots or brush. The heavier 

 sprawling Libellulid nymphs usually crawl over the bottom or climb over 

 fallen rubbish, while certain other Libellulids and some similar forms occupy 

 the mud or sand of the bottom. The nymphs of one of these latter kinds 

 is described as each scratching a hole for itself and descending into it like 

 a chicken into a dust-bath, kicking the sand over its back and burrowing 

 until all but hidden, only the tops of its eyes, the tips of its treacherous labium, 

 and the respiratory aperture at the end of the abdomen reaching the surface. 



After the few weeks or month or year which the nymph requires for its full 

 growth and development it is ready to transform. If in early summer, when 

 the dragon-flies are beginning to appear, one will go out to the dragon-fly 

 pond a little after daylight, he will see this transforming or issuance of the 



