490 THE GALL FLY. 



AU thefe apparently monftrous produflions are occafion« 

 ed bv the punclure of infe(3:s when depoiitirig their eggs, 

 or hf their bite when collecting food ; in both cafes, the 

 animals fublill upon it ; and the more they eat, the more 

 vigoroufly does the protuberance continue to grow, till 

 at lafl it forms a fort of impenetrable fortrefs, to prote£l 

 its inhabitants till they have gone through their different 

 nietamorphofis, and at lafl takenr wing. But the beft con- 

 certed fchemes of infe£ls, and of man, are unequal to fe. 

 cure either from every accident that may occur, impe- 

 netrable as the habitation of the gall fly may appear, its 

 walls are often perforated by other infefts, who depotite 

 eggs there, that are foon to become rapacious worms, and 

 to lay the dwelling wafle. 



The ancient opinion concerning the animals found in 

 thefe receptacles was, that they were fpontaneoufly pro- 

 duced from the rotten wood of the plant. Afterwards, 

 it was believed, that the roots of plants had the power 

 of fucking up, along with fap frorn the earth, the eggs 

 of infe6ls, and that thefe were animated as foon as they 

 ilopped circulation through the fibres of the tree. Even 

 the intrepid Rhedi, who combated the prejudices of his 

 age with fuccefsful boklnefs, had recourfe to a kind of 

 yegitative foul in plants, by which he accounted for the 

 produftion of thefe animals. Malphigi at laft explained 

 their true origin, from eggs dt-politcd there by thofe of 

 this kind. The fame naturalift gives an ingenious ac- 

 count of the formation of thtfe escrefcenccs themfelves 



» 



by means of a liquor depolited by the fly, mixing with the 

 fap of the tree, and cauflng a fermentation at the part. 

 The fimple extravafation of juice from the wounded 



plant, 



