THE O DO NAT A 71 



at the bottom of the water and are carnivorous, feeding on larger and 

 larger animals as they grow, individuals of the largest species attacking 

 small fish in some cases, though the bulk of their food is undoubtedly 

 the aquatic larvse of insects. They lie on the bottom waiting for their 

 prey to come within reach, and when it is near enough they thrust out 

 the under-lip (labium) and seize it (Fig. 42). This labium has been 

 remarkably developed from its usual form, being drawn out into two long 

 pieces with a pair of jaws or claws at the end. When not extended the 

 piece connected at one end with the head is bent backward under the 

 body, while the second piece, hinged to the other end of the first, extends 

 forward so that its front end with the jaws lies near the front of the head, 

 which it somewhat conceals, and this has led to calling the structure a 

 "mask." When this is extended forward it reaches out more than twice 

 the length of the head, thus enabling the nymph to capture animals which 

 are not very close to it. 



Breathing in the nymphs of the damsel-flies appears to be, in part at 

 least, by means of long and rather large, tracheal gills at the end of the 

 abdomen, which are also used for swimming. In the. other section of 

 the Order, the gills are found in the rectum, into which water is drawn, 

 bathing the gills there, after which it is expelled, and if this is done quickly 

 the recoil carries the nymph forward, thus providing one means of 

 locomotion. 



Molts are frequent, and when full-grown the nymph crawls out of 

 the water and molts for the last time, whereupon the wings grow to full 

 size and the adult insect is produced. Some dragon-flies have two 

 generations a year or possibly even more, while in other cases more than 

 a year is necessary to a generation, but one each season is the usual 

 condition. 



Despite tradition and their bad reputation, dragon-flies are in no 

 way injurious .to man, not stinging they have nothing to sting with 

 nor biting to such an extent as to cause the slightest pain, their jaws 

 being too weak to even break the skin. They are beneficial insects 

 both as young and adults, so much of their food consists of injurious 

 insects such as flies, mosquitoes, etc., while the injury they cause by 

 feeding on fish is usually so slight as to be negligible. 



Dragon-flies are sun-loving animals, concealing themselves during 

 dark, cloudy weather Between 5,000 and 10,000 kinds are known, and 

 the greatest number of these occur in the warmer regions. Fossil dragon- 

 flies or insects resembling them are numerous, and some of them were 

 very large, one measuring more than two feet from wing-tip to wing-tip. 



