THE GALE FLY. 
490 
All fhefe apparently monflrous productions are cccafion- 
ed by the punflure of infetts when depoliting their eggs, 
or by their bite when collecting food ; in both cafes, the 
animals fubfift upon it ; and the more they eat, the more 
vigoroufly docs the protuberance continue to grow, till 
at lad it forms a fort of impenetrable fortrefs, to protedt 
its inhabitants till they have gone tii rough their different 
metamorphofis, and at lad taken wing. But the bell con- 
certed fchemes of infedls, 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 infeds, who depoflte 
eggs there, that are foon to become rapacious worms, and 
to lay the dwelling wade. 
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 belieyed, that the roots of plants had the power 
of fucking up, along with fap from the earth, the eggs 
of infects, and that thefe were animated as foon as they 
flopped circulation through the fibres of the tree. Even 
the intrepid R/jedi, who combated the prejudices of his 
age with fuccefsful boldaefs, had recourfe to a kind of 
vegitative foul in plants, by which he accounted for the 
produ&ion of thefe animals. Malphigi at lafl. explained 
their true origin, from eggs depofited there by thofe of 
this kind. The fame naturaiift gives an ingenious ac- 
count of the formation of thefe excrefcences themfelves j 
by means of a liquor depofited by the fly, mixing with the 
fap of the tree, and caufing a fermentation at the part. 
The fimple extravafation of juice from the wounded 
plant, 
