HYMENOPTERA. TEREBRANTIA. 163 



saws, by small teeth placed on the outer side of each, so 

 that while their vertical effect is that of a saw, their 

 lateral effect is that of a rasp. In the artificial saw the 

 teeth all point outward (towards the end) and are simple, 

 but in the saw of the Tenthredo they point inward or 

 towards the handle, and their outer edge is beset with 

 smaller teeth which point outward (towards the end) ." 



When the little Sawfly has completed her incision 

 (which, according to the species, is made in various parts 

 of plants, in the stem, in the ribs of the underside of the 

 leaf, or in the edge of the leaf), the egg is passed down, 

 as has just been said, between the saws into the place 

 thus prepared for it. Now it is well known that all 

 wounds caused by a rough or blunt tool are more difficult 

 to heal than those which are " clean cut." This holds 

 good in the vegetable as in the animal subject, and it is 

 here probably that the final cause of the complicated 

 structure of this beautiful little instrument may be sought. 

 It is not desirable that the wound should heal. The 

 fissure in which the egg is inserted is not a mere resting 

 place, but is designed to afford nourishment to the eggs, 

 which, absorbing the juices of the plant, actually grow 

 between the time of their exclusion and their hatching.* 

 A supply of nourishment is thus produced and maintained 

 by the stoppage of circulation consequent on the opening 

 of this wound, which, in some cases, is further irritated 

 by the introduction, at the time of oviposition, of a drop 

 of poisonous fluid. In some cases this results in the 

 formation of an excrescence similar to that produced by 

 the Gallflies, within which the egg lives, grows, and is 



* This phenomenon is not confined to the eggs of the Tenthredinid, it 

 has been observed in those of the Ant ; nor even to those of insects, as it is 

 the case with fishes. 



M2 



