IX DRAGON-FLIES 333 



attitude. The larva clinging to a stem in the shady 

 recesses of water-weeds is not easily distinguished, 

 and the absence of movement removes the chief risk 

 of discovery. In the same way, the Hare in long 

 grass, the young Plover on a heath, the Trout in a 

 pool, are all concealed from view by their not very 

 close imitative coloration, but when they move, even 

 an ill-trained eye observes them. Until they move, 

 the eye is not focused upon them at all, but a mov- 

 ing object is noticed even when out of focus. The 

 policy of the slow Dragon-fly larva is to lie still and 



Fig. 97.— Head of larva of ^schna, in side-view, with mask projected to seize prey. 



wait till its victim comes within easy reach. Then of 

 course it must be quick as lightning. It does not 

 usually make a spring, but stretches out an arm-like 

 appendage of the head, and seizes its prey. The 

 appendage so employed is a peculiar modification of 

 a pair of limbs attached to the head, and called the 

 second pair of maxilLx.^ In Insects these appendages 

 form the third pair of jaws, and are fused more or less 

 completely into a labium or under-lip, which closes in 

 the back of the mouth. The labium of the Dragon- 

 fly larva is carried on a jointed arm, and usually 



1 Other explanations of the origin of these parts have been 

 given, and the question is not easily settled in a decisive way. 



