338 ARTICULATA. INSECTA. 



drawn. When this is retracted, the cavity becomes 

 filled with water, which by the thrusting down of 

 the piston to the extremity is forcibly expelled as 

 from a syringe ; this stream, acting on the surround- 

 ing fluid, communicates an impulse to the Insect 

 which shoots it forward several inches. This may 

 be readily witnessed, as the larvce are procured in 

 any pool in spring. The mouth is a most formid- 

 able apparatus for seizing and tearing prey ; the 

 whole face is composed of a long flat kind of mask, 

 ending in a rounded point, and divided in the middle 

 by serratures, like the teeth of a gin, which fit into 

 each other. These valves it throws open, and darts 

 to a great length by means of a double fold, 011 the 

 approach of prey, to seize it and carry it to the 

 mouth which is concealed within, the serrated teeth 

 holding it firmly while it is being devoured. 



The pupa, when fully matured, crawls out of 

 water on some tree or herb, where it remains until the 

 sun dries its skin ; this then splits down the thorax, 

 and the perfect insect comes out in its beauty, leav- 

 ing the empty pupa-case still clinging to the stalk. 

 The wings are at first very short, thick, and wrinkled ; 

 but, by the circulation of the fluids through the ner- 

 vures, they rapidly expand to their full size and 

 form, become transparent, and finally stiff and firm. 

 Then away the Demoiselle flies, to hawk to and fro 

 over the water she has just left, in pursuit of the 

 gnats and flies that throng the air. On catching 

 an insect, she invariably alights to eat it. 



The Day-flies, (Ephemera,*) noted for their brief 



, ephemeras, enduring for a day. 



