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XIII. The Galls of Essex ; A Contribution to a List of 

 THE Insect Fauna of the County. 



By Edward A. Fitch, F.L.S., Sec.Ent. Soc, &c., 



Vice-President. 



[Eead October 29th, 1881.] 



A GALL may be defined as an abnormal or morbid growth, 

 due to parenchymatous hypertrophy, and produced by the 

 pecuHar action of some unnatural or foreign agency, probably 

 through mechanical irritation. These growths occur both in 

 the animal and vegetable kingdoms. Animal galls are not 

 common, unless we include the various inflammatory growths 

 and excessive developments of cuticle so common in the 

 Mammalia, which are gall-like in nature, although not true 

 galls. Animal galls caused by insects, however, occur in the 

 peculiar "worbles" or "hots" often so commonly seen on 

 the backs of our young cattle ; these are produced by a 

 dipterous fly {Oestrus bovis, Linn.), which lays its eggs under 

 the skin of the bullock, and the inflammation set up produces 

 a gall in which the larva resides until full-fed.^ This is 

 hardly a true gall, as there is a small orifice communicating 

 with the open an-, but still it is as analogous as the exigencies 

 of animal and vegetable pathology will allow. Animal 

 pseudo-galls have also been produced by the action of various 

 Acaridea. Much of interest might be said about these and 

 other pseudo-galls ; but our business is with the vegetable 

 galls more particularly, and to these we will turn. 



Plant galls are fairly ubiquitous, and some kinds must be 

 known at least by sight to everyone ; these distinct abnormal 

 growths have been noticed by all naturalists or general 

 observers in one form or another, especially the galls occurring 

 on various trees, as the oak, willow, elm, or rose. 



1 Many similar swellings are produced on various animals by the 

 (Estridae. Cf. F. Brauer's ' Monographic der CEstriden.' Vienna, 1863. 



