DRAGON-FLIES 39 



adaptable thereto, so that the same nymph may be 

 brown when lying on mud, but green later if it should 

 come to rest among weeds. This chameleon-like 

 faculty, as Mr. Lucas remarks, " no doubt serves a 

 double purpose, that of hiding the nymph from its 

 enemies, and at the same time enabling it, without 

 being suspected, to approach within striking distance 

 of its prey." In fact, the nymph has none of the 

 activity which distinguishes its parents. Usually, it 

 either waits for its victim to draw near, or else creeps 

 stealthily towards it ; though it can, on occasion, dart 

 forward with considerable rapidity, propelling itself 

 by means of a jet of water expelled from the anal open- 

 ing, or (in some species) with the aid of three oar-like 

 blades which project from the extremity of the abdo- 

 men. The food of the dragon-fly nymph consists of 

 almost any aquatic creatures with which it may be 

 strong enough to cope. Some of the larger kinds even 

 attack small fish. 



Young dragon-fly nymphs breathe in one of two 

 ways. In most of the larger and heavier species, the 

 rectum, or hinder portion of the intestine, is lined with 

 gill-like folds, which receive fine branches from the 

 tracheal tubes. Water is constantly drawn in and ex- 

 pelled through the anus, and the dissolved oxygen 

 which it carries passes through the delicate cuticle of 

 the gill-folds into the tracheal system. It is by the 

 forcible expulsion of this water that these large nymphs 

 are able to propel themselves forward. In the smaller 

 and more slender species, the three oar-like plates at 

 the tail-end are really gill-structures, traversed by air- 

 tubes, by means of which gaseous exchange is effected. 

 We have seen that these plates can also be used for 

 propulsion when occasion demands. In all dragon-fly 



