GALL-FLIES. 371 



stances of the nests constructed by gall-insects, may 

 be found in abundance during the summer, on the 

 leaves of the rose-tree, the oak, the poplar, the wil- 

 low (Salix vimmalis,) and many other trees, in the 

 globular form of a berry, about the size of a currant, 

 and usually of a green colour, tinged with red, like 

 a ripe Alban or Baltimore apple. 



When this pseudo apple in miniature is cut into, 

 it is found to be fresh, firm, juicy, and hollow in the 

 centre, where there is either an egg or a grub safely 

 lodged, and protected from all ordinary accidents. 

 Within this hollow ball the egg is hatched, and the 

 grub feeds securely on its substance, till it prepares 

 for its winter sleep, before changing into a gall-fly 

 (Cynijjs), in the ensuing summer. There is a mys- 

 tery as to the manner in which this gall-fly contrives 

 to produce the hollow miniature-apples, each en- 

 closing one of her eggs; and the doubts attendant 

 upon the subject cannot, so far as our present know- 

 ledge extends, be solved, except by plausible conjec- 

 ture. Our earlier naturalists were of opinion that it 

 was the grub which produced the galls, by eating 

 when newly hatched, through the cuticle of the leaf, 

 and remaining till the juices flowing from the wound 

 enveloped it, and acquired consistence by exposure 

 to the air. This opinion, however, plausible as it 

 appeared to be, was at once disproved by finding un- 

 hatched eggs on opening the galls. 



There can be no doubt, indeed, that the mother gall- 

 fly making a hole in the plant for the purpose of 

 depositing her eggs. She is furnished with an 

 admirable ovipositor for that express purpose, and 

 Swammerdam actually saw a gall-fly thus deposit- 

 ing her eggs. In some of these insects the ovi- 

 positor is conspicuously long, even when the insect 

 is at rest; but in others, not above a line or two 

 of it is visible, till the belly of the insect be gently 



