302 f HE PHILOSOPHY 



a confiderable bulk, and the gall has arrived at its full fi^e^ 

 before the worm is hatched. This gall feems to be analo- 

 gous to the membranes which invefl: a foetus, and expand 

 m all direftions in proportion to its growth. That the eggs 

 of oviparous animals grow while in the ovarium is unlverfally 

 known ; but it is fingular that the eggs of gall-flies ihould 

 grow after being feparated from the body of the mother. 

 Thefe eggs muft undoubtedly be furnifhed with external vef- 

 fels, or a kind of roots, by which they extract juices from 

 the internal cavity of the gall. Malplghius afcribes the 

 origin of galls to a corrofive liquor introduced by the fly into 

 the wound. But Reaumur, to account for the growth of a 

 gall, thinks it unneceflary to have recourfe to any fuppofed, 

 poifonous fluids, and attributes it to the fuperabundant nutri- 

 cious juices derived to that particular part by the continual 

 adlion of the abforbent veiTels of the egg, joined to its heat,, 

 which may be compared to a little fiie placed in the center 

 of the tumour. 



Whether thefe caufes are fufiiclent to explain the growth 

 of galls, we fliall fubmit to the judgment of the reader. But, 

 that the eggs depoflted by the flies augment in flze -, that 

 worms proceed from them ; that thefe worms are nourlflied, 

 and live a certain time imprifoned in the galls ; that they 

 are there transformed into nymphs or chryfalids ; and, laftly, 

 that they are metamorphofed into the winged infects, which, 

 by gnawing an aperture through the gall, take their flight 

 in the air •, are known and incontefl:ible fadts, of the truth of 

 which every m.ui may eaflly fatisfy himfelf. Examine the 

 common oak-galls, or thofe of any other tree •, if any of 

 t-hom happen to have no aperture, cut them gently open, 

 and you are certain to And an egg, a worm, a chryfalis or, a 

 fiy : But in fuch as are perforated by a cylindrical hole, not 

 a veflige of an animal is difcoverable. The galls which make 

 an ingredient in the compofltion of ink are thick, and their 



