THE TUKNIP-FLY. 



195 



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 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 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 

 abdomen. 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. Their 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 of 

 nourishment in order to enable them to complete their development ; for it is a most 

 remarkable fact that, after the egg is deposited in the groove, it rapidly increases in size, 

 obtaining twice its former dimensions. 



In the genus Cimbex, of which an example is given in the illustration, the larvae 

 possess twenty-two feet, and have the power of discharging a translucent greenish fluid 



Cimbex feviorata 

 lihyssa pcrsunsoria. 



Ordcerus gi'jas. 

 Ichneumon grossdmts. 



from certain pores placed on the sides of the body just above the spiracles. Tins feat 

 they can repeat six or seven times in succession. When the) have eaten their way to the 

 next stage of existence, they spin a cocoon of a brownish colour and of a stringy, tough 

 consistency, and either suspend it to the branches of the tree on which they have been 

 feeding, or hide it under fallen leaves. In this cocoon they remain for a comparatively 

 short time, and then emerge as perfect insects. 



The terrible TUKNIP-FLY (Athalia centifolice) belongs to this family. The larva of this 

 species is popularly called the Nigger, on account of its black colour. A species of 

 Athalia may be seen in the engraving on page 463, and is the smallest of the three flying 

 insects at the upper part of the illustration. The larva of this species feeds upon the 

 various cabbages, eating away the whole of the soft green parts of the leaves, and only 



