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TEXT-BOOK OF ZOOLOGY 



enemies and a cloak from its prey). When its large, powerful eyes have 

 spied out a victim in the shape of an aquatic insect, a larva or the 

 like, the creature slowly creeps towards it (legs very long). When 

 still at about a third of an inch away from the unsuspecting victim, it 

 suddenly seizes it and conveys it to the powerful biting organs (mandibles 

 and maxillce). The capture is effected by means of a most peculiar 

 apparatus formed by the under lip, or lalium, and composed, somewhat 

 like the human arm, of three distinct portions. The two first elongated 

 portions (upper and lower arm) are folded on each other during repose, 

 so that the mouth from below looks as if covered by a mask. (Hence a 

 labium constructed in this fashion is described as a raptorial mask.) 

 The real organ of prehension (of which the two first portions form the 

 stalk) is formed by the third portion, which represents a pair of pincers 

 or a two-fingered hand. When the larva has approached sufficiently 

 close to its victim, it suddenly projects this apparatus and seizes the 

 unsuspecting prey. (Compare with the protrusible tongue of the chame- 

 leon and the flap-like tongue of frogs. See Fig., p. 400.) 



If we watch one of these larvae kept in confinement, we notice that it 

 but rarely comes to the surface of the water, though breathing like all 

 other insects by tracheal tubes. The exchange of gases in this case is 

 effected by very fine gill-like lamellae, in which the finest ultimate 

 branches of the tracheae terminate (tracheal gills). These lamellae in 

 the larva of the present species (as well as in those of many others) are 

 found in the terminal portion of the intestine, which consequently has 

 to be constantly supplied with a stream of fresh oxygenated water 

 (intestinal respiration). If a larva confined in a vessel of water is 

 lightly chased, it tries to escape by swimming forwards, which it accom- 

 plishes by violently ejecting water from the end of the intestine (compare 

 with cuttle-fish). If we at the same moment can manage to depress the 

 front end of the larva below the surface, we can see this water being 

 squirted up to a fair height above the surface in the form of a jet (see 

 illustration). This peculiar mode of progression is, however, only 

 employed by the creature when fleeing from an enemy. 



The metamorphosis of the larva to the perfect insect takes place 

 gradually, as in the grasshopper (see p. 394); for although larva and 

 perfect dragon-fly inhabit different media, they nevertheless lead essen- 

 tially the same (predatory) mode of life. After living for some years in 

 the water, the larva finally creeps up the stem of a water-plant, tears 

 asunder its skin, and soars aloft as a perfect dragon fly. 



