SAW-FLIES. 243 



the alternate movement of the saws enables them to do double 

 work in the same time. 



Mr. Westwood, who examined these insects very closely, 

 throws out, in his "Modern Classification of Insects/' the idea 

 which forms the subject of this book. Writing of the cutting 

 weapon of the Saw-flies, he remarks that " from its admirable 

 construction it cannot be doubted that a careful examination of 

 its various modifications might furnish ideas for improved 

 mechanical instruments." 



Mr. Gosse, in his "Evenings at the Microscope," points out 

 that, beautiful and elaborate as these instruments are, they are 

 but the sheaths of a still finer and more delicate pair of saws. 

 These secondary saws have only a few teeth on the edge, and 

 these near the point, whereas the sides are furnished with a 

 number of sharp blades, set on their edges, slightly over- 

 lapping each other, and directed backwards. There is a similar 

 structure on the ovipositor of the Sirex, as we shall see when 

 we come to treat of Boring Instruments. 



Although the saws are made expressly so that they shall not 

 stick in the wood, there are many instances known where 

 female Saw-flies have been found dead on the branches, their 

 saws still in the last groove which they have cut. I am inclined 

 to think that these must be females which have deposited all 

 their eggs, and which have died, as do nearly all insects under 

 similar circumstances. This opinion is strengthened by some 

 observations made by Mr. J. K. Lord on the Cicada, the female 

 of which is furnished with a similar ovipositor :— - 



" I was curious to watch the female depositing her eggs. 



" She first clasps the branch on both sides with her legs, and 

 with the ends of the file very carefully slits up the bark. 

 Then, placing the instrument longitudinally, she files away 

 until she has obtained sufficient length and breadth. The 

 small teeth of the files are now used crosswise of this fissure, 

 until a trench is made in the soft pith. 



" When large enough, slowly down the groove in the centre 

 of the instrument glides a small pearly egg, pointed at both 

 ends, and so transparent that the little grub within is clearly 

 discernible. Gently she lays it within its bed, and then drops 

 a thin gummy material on it, to secure it from moisture. This 

 finished, she proceeds to deposit another, and so on, until a 



r 2 



