58 BRITISH TYROGLYPHID^. 



joint lias a form very similar to that of the third leg of 

 the male Ifhizoglyphus, and is used for climbing 

 purposes ; but it is evidently the whole tarsus because 

 it bears a distinct separate claw, although of an 

 exceptional character. 



Some authors do not use any names for the joints of 

 the legs in Acarina, but simply number them from the 

 proximal to the distal end. I have, however, in this 

 book preserved the same nomenclature which I used 

 for those of the Oribatidae. I think that on the whole 

 it is better, as the names convey an idea of the func- 

 tion, and the special joint referred to is usually more 

 easily identified by the name than by a number. 

 These names, beginning at the proximal end, are 

 firstly, the coxa ; secondly, the femur ; thirdly, the 

 genual ; fourthly, the tibia ; and fifthly, the tarsus. 



The Coxa is usually a more or less hemispherical 

 or shield-shaped joint, having almost universal motion ; 

 it is usually supported by an epimeron embedded in 

 the cuticle from whence inter alia various muscles arise 

 to communicate the motion. 



The Femur varies greatly in importance in different 

 species, but on the average it is not such a powerfully 

 developed joint as it is in the Oribatidse, where it is 

 almost always the principal joint of the leg. In the 

 Tyroglyphidas it is frequently less thick and strong 

 than the genual. In Aleurobius farinse it is the joint 

 which bears the holding apophysis in the first leg of 

 the male, and is far the most powerful joint : in most 

 legs of the genera Tyroglyphus and Rliizocjlyplms it is 

 either of the first importance, or only second to the 

 genual; in Glycyphagus spinipes, G. domesticus, G. 

 dispar, and many other species it is not by any means 

 a principal joint. 



The Genual, which is almost always a small joint in 

 the Oribatidas, is frequently one of the largest, and 

 sometimes actually the largest, in the TyroglyphidaB. 

 Not that it is as long as the tarsus, or indeed often as 

 some of the other joints, but it is often very much 



