ANATOMY. 53 



THE MOUTH AND TROPHI. 



The Mouth is usually a moderate- sized opening in 

 the underside of the anterior part of the cephalothorax. 

 Occasionally, as in the exceptional genus Lentungula, 

 it may be practically at the actual anterior end. It is 

 very simple compared with that of some other families 

 of Acarina. Its trophi consist of the mandibles, the 

 maxillary lip and maxillae, the maxillary palpi ; and 

 finally, in some cases, a more or less rudimentary 

 lingua. I have not detected any epipharynx, an organ 

 highly developed in some Acari, <>. g. Bdella. 



The Mandibles are always chelate, except in the 

 one genus, Histiostoma ; they are usually short and 

 thick in form, and are always set so that the fixed arm 

 of the chela is the dorsal one, and the moveable arm 

 works perpendicularly, not sideways as in most non- 

 acarine Arachnida, such as scorpions, etc. They closely 

 resemble the mandibles of the Oribatidse and of the 

 Sarcoptidas ; they most commonly have three or four 

 teeth on each arm of the chela. They are moderately 

 retractile, but not nearly so much so as those of some 

 predatory Acari such as the Gamasidae ; they are 

 manifestly tearing and crushing organs. A short indi- 

 cation of the muscles by which the mandibles are 

 worked will be found in the section of this chapter on 

 musculation (p. 120). Illustrations of the mandibles 

 will be found in the plates of almost every species, and 

 their musculation is shown in PL C, fig. 1 ; and the 

 part that is contained within the mandible itself in 

 PL I, fig. 7 (LeittuHf/ula), and in the mandible of 

 Cliortoglyphus arcuatus (vol. ii). 



In most species the rostrum is usually held sloping 

 downward, or even perpendicularly downward in some 

 cases. Thus the dorsal, or upper, edge of the mandible 

 becomes the anterior in ordinary position, but this may 

 be altered at any moment in most cases. In such a 

 species as G t (U'r.inrfus, where the mouth and trophi are 

 almost enclosed in a stiff chitinous hood; which is 



