542 SAW-FLIES, 
bits of shells, or even small living shells, in which it lives in perfect 
security, and crawls about in search of food, dragging its house after it. 
When it is about to become a pupa, it spins a strong silk grating over the 
entrance of its case, so that the water necessary 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 bite. 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 in- 
sect 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, 
transparent, membranous, the veins compara- 
tively few, and the hinder pair smaller than 
the others. Their mouth is furnished with 
powerful horny jaws, and with a tongue guard- 
ed by the modified maxilla. 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 proceed at once to the 
Rhyssa persuasoria. family of the Tenthredinidz, or SAW-FLIES. 
. In this and the next family, the females 
are furnished with a peculiar ovipositor, composed of several pieces. 
The true Saw-flies are known by the curious piece of animal mechanism 
from which they derive their name. The females of this family are supplied 
Cimbex femorata, Urocerus gigas, 
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 particular species to 
