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CHAPTER XX. 



AXIMAL GALLS,* PRODUCED BY BREEZE-FLIES AND SNAIL-BEETLES. 



The structures which we have hitherto noticed have all 

 been formed of inanimate materials, or at the most of grow- 

 ing vegetables ; but those to which we shall now advert 

 are actually composed of the flesh of living animals, and 

 seem to be somewhat akin to the galls already described as 

 formed upon the shoots and leaves of plants. These were 

 first investigated by the accurate Vallisnieri, and subse- 

 quently by Reaumur, De Geer, and Linnaeus ; but the best 

 account which has hitherto been given of them is by our" 

 countryman Mr. Bracey Clark, who differs essentially from 

 his predecessors as to the mode in which the eggs are 

 deposited. As, in consequence of the extreme difficulty, if 

 not the impossibility, of personal observation, it is no easy 

 matter to decide between the conflicting opinions, we shall 

 give such of the statements as appear most plausible. 



The mother breeze-fly ( Oestrus bovis, Clark ; — Hypoderma 

 bovis, Latr.), which produces the tumors in cattle called 

 wurbles, or wormuls {quasi, worm-holes'), is a two-winged insect, 

 smaller, but similar in appearance and colour to the carder- 

 bee (p. 54), with two black bands, one crossing the 

 shoulders and the other the abdomen, the rest being covered 

 with yellow hair. This fly appears to have been first dis- 

 covered by Vallisnieri, who has given a curious and inter- 

 esting history of his observations upon its economy. " After 

 having read this account," says Reaumur, "with sincere 

 pleasure, I became exceedingly desirous of seeing with my 

 own eyes what the Italian naturalist had reported in so 



* In order to prevent ambiguity, it is necessary to remark that the 

 excrescences thus called must not be confounded with the true galls, 

 which are occasionally found in the gall-bladder. 



