134 INSECT ARCHITECTURE. 



currant trees of their leaves, and are no less destructive to 

 birch, alder, and willows ; while turnips and wheat suffer 

 still more seriously by their ravages. These grubs may 

 readily be distinguished from the caterpillars of moths and 

 butterflies by having from sixteen to twenty- eight feet, by 

 which they usually hang to the leaf they feed on, while they 

 coil up the hinder part of their body in a spiral ring. The 

 perfect flies are distinguished by four transparent wings ; 

 and some of the most common have a flat body of a yellow 

 or orange colour, while the head and shoulders are black. 



In order to see the ovipositor, to which we shall for 

 the present turn our chief attention, a female saw-fly must 

 be taken, and her belly gently pressed, when a narrow 

 slit will be observed to open at some distance from the 

 apex, and a short, pointed, and somewhat curved body, 

 of a brown colour and horny substance, will be protruded. 



o. Ovipositor of Saw-fly, prutnuled lioni its slieath, magnified. 



The curved plates which form the sides of the slit, are 

 the termination of the sheath, in which the instrument 

 lies concealed till it is wanted by the insect. The appear- 

 ance of this instrument, however, and its singular struc- 

 ture, cannot be well understood without the aid of a micro- 

 scope. 



The instrument thus brought into view is a very finely- 

 contrived saw, made of a horny substance, and adapted 

 for penetrating branches and other parts of plants where 

 the eggs are to be deposited. The ovipositor-saw of the 

 insect is much more complicated than any of those em- 

 ployed by our carpenters. The teeth of our saws are 

 formed in a line, but in such a manner as to cut in two 



