632 



THE SAW-FLIES. 



for its respiration can pass through, but at the same time all enemies 

 are kept out. When the time for its change has arrived the pupa 

 bites through the grating, rises to the surface, and crawls out of the 

 reach of the water, which would soon be fatal to it. The skin then 

 splits down the back, and the perfect insect emerges. 



The order is called Trichoptera, because the wings, instead of being 

 covered with scales, as are those of butterflies, are clothed with hairs. 

 There are many species of Caddis-flies. 



We now come to the vast order of insects technically called the 

 Hymenoptera. In these insects the wings are four in number, trans- 

 parent, membranous, the veins comparatively few, and the hinder pair 

 smaller than the others. Their mouth is furnished with powerful horny 

 jaws, and with a tongue guarded by the modified maxillae. The females 

 are armed with a many-valved sting or ovipositor. In this enormous 

 order are included all the bees, wasps, and their kin, the great family 

 of saw-flies, the ichneumons, the gall-flies, and the ants. We will pro- 

 ceed at once to the family of the Tenthredinid^, or Saw-flies. 



In this and the next family 

 the females are furnished with 

 a peculiar ovipositor, compos- 

 ed of several pieces. 



The true Saw-flies are known 

 by the curious piece of animal 

 mechanism from which they 

 derive their name. The fe- 

 males of this family are sup- 

 plied with a pair of horny 

 saws, placed side by side on 

 the lower extremity of the 

 abdomen. 



These saws are of various 

 forms, according to the par- 

 ticular species to which they 

 belong, and may be seen even 

 in the dried specimens, the top of their sheath slightly projecting, and 

 their shapes plainly visible after the removal of a portion of the abdo- 

 men. When taken from the insect and placed under the microscope 

 they present a very pretty appearance, owing to the gently-curved ribs 

 with which their sides are strengthened and decorated. The saws act 

 alternately, one being pushed forward as the other is being retracted, 

 rheir object is to form a groove in some plant, in which the eggs of 

 the mother-insect can be deposited, and wherein they shall find a supply 

 ot nourishment in order to enable them to complete their development ; 

 lor It IS a most remarkable fact that after the egg is deposited in the 



The Sirex Gigas. 



