458 ARACHNIDA—ACARINA CHAP. 
p- 467), which are nearly all covered by an extremely hard and 
coriaceous armature. 
Eyes are sometimes absent, sometimes present in varying 
numbers. They seem here to be of remarkably little systematic 
importance, as otherwise closely allied species may be either 
eyed or eyeless. 
Normally Mites possess the usual Arachnid appendages, 
chelicerae, pedipalpi, and four pairs of ambulatory legs. The 
anterior appendages are, however, subject to a very great degree 
of modification, while in one Family, the Eriophyidae (Phytop- 
tidae), the legs are apparently reduced to two pairs. 
The chelicerae are sometimes chelate, in which case they are 
two-jointed, the distal jomt or movable finger being always 
articulated below the immovable finger. Sometimes they ter- 
minate ina single claw or blade, the movable joint being obsolete. 
In the Ticks they exist as two long styles or piercing weapons, 
serrate on the outer edge. 
The pedipalpi vary very much in structure, according to the 
habits of the particular form to which they belong. . In the 
Sarcoptidae (see p. 466) they are hardly recognisable owing to 
the extent to which they have coalesced with the maxillary 
plate. In many of the free-living forms they are leg-like feeling 
organs, but in others they are raptorial, being not precisely 
chelate, but terminating in a “ finger-and-thumb ” arrangement 
which is of use in holding prey. The extreme development of 
the raptorial palp is found in Cheyletus (see p. 473), in which 
the whole appendage is remarkably thick and strong, and the 
“finger” is a powerful chitinous claw, while the “thumb” is 
replaced by movable pectinated spines of chitin. The Water-mites 
have a palpus adapted for anchoring themselves to water-weeds, 
the last joint being articulated terminally with the penultimate 
joint, and bending down upon it. Finally, in the “ Snouted- 
mites” (Bdellidae, see p. 471) the palpi are tactile or antenni- 
form, often strongly recalling the antennae of weevils. 
The maxillary plates which arise from the basal joints of the 
pedipalps are always more or less fused, in the Mites, to form a 
single median transverse plate, constituting the lower lip or 
“Jabium” of some authors. In some of the Oribatidae the 
fusion of the maxillae is only complete at the base, and the free 
points are still of some use as masticating organs. In those free 
