CH. XVII.] VARIOUS SPECIES OF SAWFLIES. 247 



fifty different species of them to be found in 

 Great Britain, opportunities for investigating their 

 habits and economy are not wanting to those who 

 may be desirous of verifying our account of them. 

 The perfect insects are generally found upon various 

 kinds of plants, upon or within which the females 

 deposite their eggs, and which they are instructed by 

 instinct to place in small grooves formed in the 

 bark, wood, or leaves of the plant, upon which the 

 future progeny are to be nourished. It is neces- 

 sary, therefore, that the female should be furnished 

 with an instrument capable of making a proper in- 

 cision, and we accordingly find the ovipositor admi- 

 rably formed for this purpose. The under surface 

 of the body exhibits near its extremity a narrow 

 slit, formed of two horny, jointed grooves or sheaths, 

 between which, when unemployed, the ovipositor 

 or auger itself lies concealed ; when, however, the 

 insect wishes to deposite her eggs, she bends the 

 extremity of the body downwards and inwards, pro- 

 truding the instrument at an angle with the body 

 from the base of the slit formed by the two grooves. 

 The ovipositor itself is composed of two broad but 

 very thin saws, which are projected and withdrawn 

 by the female during the act of cutting the channel 

 in which the eggs are to be placed, by the assist- 

 ance of strong muscles at the base of each saw. 

 These saws do not act in concert together, but 

 while one is pushed forward the other is withdrawn 

 from the incision made in the stem or bark. This 

 appears to us to be owing to the circumstance of 

 the saw, which remains in the slit, serving the pur- 

 pose not only of a saw, but also of a wedge, keep- 

 ing the mouth of the channel open until the other 

 saw is thrust deeper into the wound. These two 

 saws are not straight, like handsaws used by car- 

 penters, but are of a curved form, somewhat like a 

 flattened S. Like the common handsaw, each of 

 these saws is lodged in a distinct piece, formed of 



