ANATOMY 



459 



prg 



living Mites which have undergone no great modification of the 

 mouth parts two other portions can be distinguislied, the upper 

 lip or " epipharynx," and the " lingua," which forms the floor of the 

 mouth, and is for the most part concealed by the maxillary plate. 



The legs are usually six- or seven-jointed, and are subject to 

 great variation, especially as regards the tarsus or terminal joint. 

 This may bear claws (1-3) or sucking disks, or a combination of 

 the two, or may simply take the form of a long bristle or hair. 



The Cheese-mite has a claw surrounded by a sucker — like 

 Captain Cuttle's hook within his sleeve. The claws of those 

 species which are parasitic on the hairs of animals are sometimes 

 most remarkably modified. 



Internal Structure. — The minute size of most Mites has 

 rendered research upon their internal structure a matter of great 

 difficulty, and there are still many obscurities to be removed. 

 Those forms which have been sub- 

 jected to examination present a 

 tolerable uniformity in the structure 

 of the principal organs, but the brief 

 description here given will not, of 

 course, apply to aberrant groups 

 like the Vermiformia. A marked 

 concentration is noticeable through- 

 out the Order, and is best exempli- 

 fied by the nervous system. 



The mouth leads into a sucking 

 pharynx, which narrows to form the 

 oesophagus. This passes through 

 the nerve - mass in the 

 Arachnid fashion, and widens to 

 form the ventriculus or stomach. 

 The oesophagus varies considerably 

 in width in the various groups, 

 being very narrow in those Mites 

 which merely suck blood, but wider in vegetable -feeders like 

 the Oribatidae. 



The stomach is always provided with caeca, but these are not 

 nearly so numerous as in some other Orders of Arachnida. 

 There are always two large caeca directed backwards, and there 

 may be others. They are most numerous in the Gamasidae (see 



,,„,,„i Fig. 239. — Diagram of tlie viscera of 

 an Oribatid Mite, greatly enlarged. 

 C, C, Lateral caeca of stomach ; g, 

 cerebral ganglion ; od, od, oviducts ; 

 oe, oesophagus ; lir.g, pro-ventri- 

 cular gland ; ps, pseudo-stigmatic 

 organ ; st, stomach ; tr,tr, tracheae. 

 (Partly after Michael.) 



