XXII SAWFLIES 513 



lower aspect of the hinder extremity of the body, where they 

 are enclosed and protected by a pair of sheaths, from which 

 they can be made to protrude by a little pressure exercised on 

 the parts immediately in front of them. Each female possesses 

 a pair of these saws ; they consist of thin laminae of very 

 hard consistence, and are not only toothed at their edge, but in 

 many cases each tooth is itself serrate ; at the same time the 

 outer face of the saw is sculptured or plicate in a remarkable 

 manner, so that the saw in this way acts as a file or rasp. The 

 Insect having selected a suitable place, uses the saws by placing 

 the extremity of the abdomen against a twig or leaf, protruding 

 the blades, which, moving with an alternate motion, one being 

 thrust forward while the other is retracted, act on the plant so 

 as to make an incision. Each saw is directed in its movement by 

 the support, the pair of supports being united at the base by 

 membrane as shown in Eig. 344. In the case of some species, 

 Hylotoma rosae, the common sawfiy of our rose-bushes, for 

 instance there is no difficulty in observing the operation ; in- 

 deed old Eeaumur, when speaking of the placid disposition of the 

 sawflies, suggests that it was given them so that we may easily 

 observe their charming operations. We cannot but regret that 

 in these days we are unable to take so complacent a view of the 

 arrangements of nature. There is much variety in the details 

 of the structure of these saws ; so much indeed that it is possible 

 to identify most of the species by means of the saw alone. 

 According to certain observers, the eggs are laid by some kinds 

 on, not in, the leaves, so that we may conclude that in , these 

 cases the saws are not used by their possessors. An incision 

 having been made, an egg is placed in it, and also a drop of some 

 liquid matter. The egg is at first small, but soon increases til] 

 it becomes twice or three times its former size, and the develop- 

 ment of the embryo commences. 



The larvae of the Tenthredinidae exhibit great variety, and 

 are indeed in this respect more interesting than the perfect 

 Insects. The usual rule is that the larvae much resembles 

 those of Lepidopterous Insects, and feed exposed on plants in 

 the same way as Lepidopterous larvae do. But the exceptions 

 are numerous ; sometimes the larva is covered with slime, and 

 thus protected from various enemies. In other cases it is very 

 depressed, a broad creature, of irregular outline, living closely 



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