insects: stings and ovipositors. 129 



the oak, are not the proper fruit of the tree, but diseased 

 developments produced by a tiny insect, for the protec- 

 tion and support of her young. Kirby and Spence tell 

 us that the parent fly introduces her egg into a puncture 

 made by her curious spiral sting, and in a few hours it 

 becomes surrounded with a fleshy chamber. Mr. Yirey 

 says the gall-tubercle is produced by irritation, in the 

 same way as an inflamed tumour in an animal body, by 

 the swelling of the cellular tissue, and the flow of liquid 

 matter, which changes the organisation, and alters the 

 natural external form. 



Perhaps a still more charming example of animal 

 mechanics is that' furnished to us by the Saw-flies 

 (Tenthredinidce). These are very common four-winged 

 insects of rather small size, many species of which are 

 found in gardens and along hedges in summer, produced 

 from grubs which are often mistaken for true caterpillars, 

 as they strip our gooseberry and rose bushes of their 

 leaves; but which may be distinguished from them by 

 the number of their pro-legs, and by their singular 

 postures; for they possess from eight to fourteen pairs 

 of the former organs, and have the habit of coiling up 

 the hinder part of their body in a spiral ring, while they 

 hang on to the leaf by their six true feet. 



These saw-fly caterpillars are produced from eggs 

 which are deposited in grooves made by the parent fly 

 in the bark of the tree or shrub whose future leaves are 

 destined to constitute their food ; and it is for the con- 

 struction of these grooves, and the deposition of the 

 eggs in them, that the curious mechanism is contrived 

 which I am now bringing under your notice. 



Almost all our acquaintance with this instrument and 

 the manner of its employment, we owe to the eminent 

 French naturalist, Reaumur, and to his Italian con- 

 temporary, Valisnieri. Their details I shall first cite, as 

 they have been put into an English dress by Kennie, and 



K 



