THE DRAGON-FLIES. 



203 



Like the other aquatic Neuropterous larvae and 

 pupae, those of the Dragon-flies are aquatic in their 

 respiration, but in the larger species of the group, or 

 those in which the wings of the perfect insect are 

 always extended horizontally^ this function is per- 

 formed in a very singular manner* They have no 

 external branchiae, but at the extremity of the body 

 we find an apparatus of five horny plates, which, when 

 laid together, close the anal orifice. When these are 

 opened, however, the water rushes into the dilated 

 extremity of the intestinal canal, where it comes in 

 contact with the tufted branchiae enclosed in that 

 cavity ; and when these have deprived it of its air, it is 

 again expelled by the contraction of the walls of the 

 intestine. So great is the force with which this ex- 

 pulsion is effected, that it may be seen to move the 

 particles of mud at a distance of two or three inches 

 from the anus, and its recoil is sufficient to propel 

 the insect slowly through the water. In the slender- 

 bodied Agrions, on the contrary, the larvae and pupae 

 are furnished with three leaf-like gills at the extre- 

 mity of the abdomen, and by the action of these they 

 are also enabled to swim through water, in the same 

 way as a fish. 



The Dragon- flies occupy nearly a year in passing 

 through their preparatory states, and when the time 

 for their final transformation arrives, the pupae creep 

 up the stem of some aquatic plant until they are 

 above the surface of the water, when they attach 

 themselves firmly by their claws, and prepare for 

 their last great change. In a short time the skin of 

 the back of the thorax splits longitudinally, and the 

 enclosed insect soon disengages the anterior part of 

 its body from its envelope by bending the head back- 



