298 INSECTS AT HOME. 



At the extremity of the abdoraen and on its under surface 

 are placed two flat horny plates set side by side. These are 

 the saws, and, like the well-known ' tenon-snw' of carpenters, 

 have one edge toothed, and the other strengthened by a flat 

 thick plate. On examination with a tolerably powerful lens, 

 the teeth are seen to be most elaljorately constructed. Instead 

 of being mere simple teeth, like those of a saw, each tooth is 

 formed of a cone set in a footstalk, the cone being deeply cut 

 into eight or ten deep grooves, having a sharp edge between 

 each. This structure is wonderfully adapted to prevent the 

 saw from clogging with the green wood in wJiich it has to work, 

 and might with advantage be copied by our tool-makers. The 

 toothing of the saw differs in the various species of Saw-fly, 

 but the form which has been described is found in some of the 

 insects with which our list commences. 



The strengthened backs of these saws are received into grooves 

 or sheaths in which they slide backwards and forwards, and they 

 are so contrived that while one saw is being thrust forward, 

 the other is being drawn back. There is not the least difficulty 

 in getting these beautiful instruments under the microscope. 

 They are of course best seen in the recent specimen, but even 

 after the insect has been long dead and dry, the saw can be 

 detached with a little careful manipulation. The object of the 

 saw, which is indeed a modification of the ovipositor, is to pre- 

 pare a resting-place for the eggs. By alternately working the 

 saws, a groove is rapidly cut in a twig, or a leaf rib, and an 

 e(fg is then passed between the saws and deposited in the groove, 

 , where it is fixed by a small drop of liquid secreted by the insect. 

 The number of grooves and of the eggs deposited in them 

 varies according to the different species of Saw-fly. Even if the 

 observer shoidd foil to see a Saw-fly in the act of depositing 

 her eggs, he can always see the grooves and the eggs in them, 

 by carefully examining the leaves and young twigs of various 

 trees. The common currant is often much damaged by Saw- 

 flies, and on a single bush there will be scarcely a leaf in 

 which the grooves cut by the Saw-fly cannot be found. These 

 grooves are made on the under side of the leaf, partly because 

 the nervures are thicker, and partly because the eggs are 

 sheltered from the rain. 



In process of time the eggs are hatched, and from them are 



