DRAGON-FLIES. 11 



although carnivorous like the perfect insect, they are 

 very sluggish in their movements. They lurk amongst 

 water- weeds or mud in stagnant pools, and capture their 

 prey by means of a peculiar structure termed the mask. 

 This organ is apparently formed by a backward growth 

 of the bases of the labium and lingua, a hinge being 

 formed between the two, at the most posterior point of 

 their growth. The prolonged portions of these parts are 

 free ; usually the mask is folded under the head, but it 

 can be unfolded and thrust forward with great rapidity. 

 The front parts of the labium form a prehensile appa- 

 ratus armed with sharp teeth, so that the structures 

 make altogether a very effectual trap, that can be ex- 

 tended in order to secure the prey (see Plate III., figs. 3- 

 and 6). 



The respiratory organs of dragon-fly larvae are very 

 remarkable. In the nymphs of the Anisopterides a large 

 number of minute gills is situated in the rectum, and these 

 gills obtain air from water admitted into the rectum for 

 the purpose. The extremity of the body is armed with pro- 

 jections of variable form that can be separated to allow 

 ingress and egress of the fluid, or brought together so as 

 to close the orifice. The water, so taken in, can, by some 

 species, be ejected with force, and is used occasionally as 

 a means of locomotion. These rectal gills can absorb 

 free air, as well as air dissolved in water ; if the water in 

 which the creatures are placed does not contain sufficient 

 air the nymphs thrust the extremity of the body above 

 the surface and thus obtain a supply. 



In the larvae of the Zygopterides rectal branchiae do 

 not exist and respiration seems to be partly effected by 

 means of three mobile processes at the extremity of the 

 body, and partly by ordinary spiracles. 



Ten species of dragon-flies are at present known in 

 New Zealand, but of these only four can be called at all 

 common. 



The number of insects killed by dragon-flies, in places 

 where they are abundant, must be enormous ; the nymphs, 

 too, are very destructive in the waters they inhabit, so 

 that dragon-flies have no doubt been no mean factor in 

 maintaining that important and delicate balance of life 

 which it is so difficult to appreciate. The nymphs are no 

 doubt cannibals ; and this may perhaps be an advantage 

 to the species, as the eggs are sometimes deposited in 

 large numbers in a limited body of water where all must 

 perish if the nymphs did not, after exhausting other food r 



