370 THE NATURAL HISTORY 



but when they are brought into use, they are slightly 

 separated so as to work freely and rapidly side by side 

 alternately, and the saws are made to " clear " them- 

 selves, as the carpenters express it, by means of the 

 transverse ridges on the outer surface of each it will 

 thus be evident that they act as saws and rasps at the 

 same time. As may be anticipated, there are differences 

 of detail in the ovipositors of the various species, but 

 the general plan of construction is the same through- 

 out the whole family. With these beautifully-finished 

 implements, the flies not only make fine saw-cuts in 

 the tender bark of trees, or the leaves of plants, but 

 they afterwards delicately and surely guide an egg 

 between them down into the incision they have thus 

 made. A drop of fluid is then introduced into the 

 wound, the probable effect of which is to keep it open 

 till the larva is hatched out ; in the meantime the egg, 

 unlike those of the majority of insects, absorbs moisture 

 from" the substance in which it is deposited, and in- 

 creases considerably in size. 



Among the numerous individuals of this group 

 which we have met with here, by far the most remark- 

 able for its size and beauty, is the Cimbex lutea ; this 

 handsome fly is not much unlike a small hornet in 

 general appearance, and we have taken three or four 

 specimens, one of which is still in our possession. The 

 larvae of Trichiosma lucorum we have frequently shaken 

 off the whitethorn in the now obsolete hedgerows, we 

 have also found its cocoons in the winter and kept 

 them, under the impression that they were those of a 

 moth, till the perfect fly made its appearance and 

 undeceived us. Abia sericea is a strikingly glossy 

 brassy-green fly, with yellowish legs and antennce, of 

 which we have captured three or four specimens on the 

 blossoms of umbelliferous plants, but we have never 

 identified its larva. Hylotoma Roses is sufficiently com- 

 mon to have more than once brought down upon its 

 larvae the vengeance of the gardener ; Allantus Scro- 



