Dragon-Flies 



When the eggs hatch the young immediately begin an active, 

 predatory life under the water, feeding upon other aquatic in- 

 sects. This food habit is continued throughout their larval or 

 nymphal existence, and as they grow larger they are able to over- 

 power larger and larger insects and even small fish and other 

 aquatic animals. They will kill others of their own kind, and 

 nymphal dragon-flies have been seen to catch and destroy adults 

 in which the wings were not yet expanded. They molt probably 

 a number of times, but the exact number has not been recorded 

 for any species, so far as I know. The most peculiar feature of 

 the larva or nymph is the strange modification of the mouth. 

 There has been a backward growth of the lower lip and this has 

 become hinged so as to form a long, hinged apparatus with 

 sharp teeth at its extremity. It can be folded to cover the lower 

 face like a mask. The structure has been called a mask, and 

 when it is folded the head of a dragon-fly larva seen from the 

 front looks like that of a bulldog. It is more innocent looking 

 than that of a bulldog simply because we know what a bulldog 

 can do, but the moment that the larva approaches near enough to its 

 prey the innocent looking mask is unfolded and darted out, and 

 the probably unsuspecting aquatic insect or small fish is seized 

 by the teeth at the extremity and drawn back into the mouth. 



Dragon-fly larvae breathe in a peculiar way modified to some 

 extent with the members of the different families. The rectum 

 is furnished with very many tracheal branches, forming 

 numerous loops and even penetrating the walls of the intestine. 

 Water is sucked into the rectum, and these " rectal gills," as they 

 are termed, derive their oxygen from this water. This same 

 feature affords with some species a means of locomotion, for this 

 water which is sucked in for breathing purposes may be ejected 

 violently, the effect of which is to send the larva ahead. This 

 same principle has been used in certain mechanical toys, and ap- 

 plications have even been made for patents on a similar method 

 of propulsion for vessels. With some there are external abdomi- 

 nal gills, both lateral and caudal, while when the nymph be- 

 comes full grown and is ready to leave the water breathing is 

 taken up by certain obscure spiracles. There is still some doubt 

 as to the exact method by which they begin to breathe air after 

 leaving the water, and it is a subject which will bear much fur- 

 ther investigation. 



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