204 NATURAL HISTORY. [cH. XI. 



these acari has a sort of tube issuing from its tail, 

 which is funnel-shaped at both ends. The loose ex- 

 tremity is applied so firmly to the insect to be sucked, 

 that it cannot be removed even by the acarus itself 

 without great exertion. 



Of the mites which infest vegetables, our gardens 

 furnish innumerable examples. The little green- 

 ish creatures which cover the leaves with a thin 

 film, and lodge in it in myriads, ruining our fruits 

 and garden-stuff, are too well known to require de- 

 scription. 



Besides these various species of stationary acari, 

 which perish when the animal or vegetable on which 

 they feed perishes, there are others called wanderers, 

 which are common both to plants and animals. Of 

 this description is the acarus autumnalis, or harvest- 

 bug. This is a little red insect, which creates a fu- 

 rious itching wherever it buries itself. 



What the gall-fly does to a plant, the gad-fly 

 (nestrus) does to our cattle : it deposites its egg under 

 the skin of the animal, and thus gives rise to what 

 may be justly termed an animal gall. These tu- 

 mours are to be found most frequently on young and 

 well-fed calves ; and far from being" any drawback 

 in the estimation of the purchaser, cattle-breeders 

 prefer those animals in which they exist, being well 

 aware that the instinct of the parent insect causes it 

 to place its young only where its food is most abun- 

 dant that is, under the skin of such of our cattle as 

 are full of juices and health. The tanners also pre- 

 fer those skins which abound in bot-holes, oecause 



they are the thickest and strongest. As soon as the 

 worm has quitted the egg, it finds itself in a nest, 



