BRANCH ARTHROPODA ; CLASS INSECT A : THE INSECTS *95 



Compare the young dragon-flies with the adults ; note the devel- 

 oping wings and the peculiar modification of the lower lip into a 

 protrusible, grasping organ which when at rest is folded like a mask 

 over the face. Examine the interior of the posterior part of the 

 alimentary canal to find the rectal gills. Obtain specimens of adult 

 and young May-flies. The young may be found on the under side 

 of stones in a " riffle " in almost any stream. They live also in ponds. 

 They may be recognized by reference to fig. 61. Compare adult 

 May-flies with the dragon-flies ; note the weakly chitinized, delicate 

 body-wall, and the difference in size between fore and hind wings ; 

 note the biting mouth-parts of the young and their absence or 

 presence in vestigial condition only in the adults. 



The young of both dragon-flies and May-flies may easily be kept 

 alive in the laboratory aquarium (fruit-jars or battery-jars with pond 

 water in), and their feeding habits, their swimming, their respiration, 

 and much of their development observed. The young May-flies 

 should be got from ponds, not running streams. Put one ot these 

 semi-transparent May-fly nymphs into a watch-glass of water, and 

 examine under the microscope. The movements of the gills, heart, 

 and alimentary canal, and much of the anatomy can be readily made 

 out. The emergence of the adult from the nymphal skin can be 

 seen if close watch is kept. The young dragon-flies may be seen to 

 capture and devour their prey. They may also transform into adults, 

 but for this it will be necessary to obtain nymphs nearly ready for 

 transformation. 



Among the most familiar and interesting insects are the 

 dragon-flies (fig. 58), sometimes called "devil's darning- 

 needles." They are commonly seen flying swiftly about 

 over ponds or streams catching other flying insects. The 

 dragon-flies are the insect-hawks ; they are predaceous and 

 very voracious, and are probably the most expert flyers 

 of all insects. There are many species, and their bright 

 iridescent colors and striking wing-patterns make them 

 very beautiful. The young dragon-flies (fig. 59) are 

 aquatic, living in streams and ponds, where they feed 

 on the other aquatic insects in their neighborhood. 

 They catch their prey by lying in wait until an insect 

 comes close enough to be reached by the extraordi- 

 narily developed protrusible grasping lower lip (fig. 60). 

 When at rest this lower lip lies folded on the face so as 

 to conceal the great jaws. The young dragon-flies breathe 



