844 



CLASS V. ARACHNIDA. 



Many of them live parasitically on both plants and animals or 

 on decaying organic matter. They vary greatly in shape, some 

 being elongated, but perhaps their commonest form is a rounded 

 oval more or less arched dorsally and flattened on the ventral 

 surface (Fig. 554). The abdomen is as a rule separated from the 

 cephalothorax by a line or by a shallow groove, never by a deep 

 constriction. The anterior segments may be separated off from 

 the rest of the cephalothorax and when this is the case they 

 constitute the " capitulum." Many mites are blind but many 

 have numerous eyes. The number of these however varies 



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capriciously and is little used in classification. The cuticle is 

 usually soft, but is hard and thick in the Oribatidae. It bears 

 numerous hairs and markings and is sometimes highly coloured. 

 The chelicerae may be chelate with the movable claw ventral 

 to the fixed. Frequently, however, they are much modified, 

 and in some groups they are reduced to piercing stylets with 

 or without serrated edges. The pedipalps, which comprise 



more than five joints, are subject to great 

 diversity of form but are usually leg-like, 

 sometimes ending in a raptorial claw cap- 

 able of holding prey ; occasionally they 

 become almost aiitenniform. Their basal 

 joints unite in the middle ventral line 

 behind the mouth, constituting the so- 

 called labiuni. Except the Eriophyidae 

 (Phytoptidae) which have but two pairs of 

 legs, (Fig. 555) mites have the usual 

 Arachnid arrangement, viz. four pairs. 

 The legs are six- or seven-jointed as a rule, 

 though there is much variation on this 

 point, and they may end in claws (1-3), 

 suckers or hairs or some combination of 

 these organs. The claws are often beauti- 

 fully adapted to the needs of the animal, 

 fitting for instance exactly round the 

 hairs of the mammal on which the mite is living. The ab- 

 domen may be rounded or elongate (Demodex) and it is then 

 sometimes ringed (Fig. 567). 



The mouth is usually small and it leads, at any rate in some 

 species, into a sucking pharynx, whence arises a fine oesophagus 



FIG. 555. Female of Erio- 

 phyes vitis, from the leaf 

 of the vine (after H. Lan- 

 dois). Ov Ovaries : A 

 anus ; Go genital opening ; 

 .Si", iv third and fourth 

 pair of legs. 



