P. A. Buxton 
127 
mounted specimens, especially those which have been exposed to some 
pressure, it is frequently pushed to the side; it then becomes more easily 
seen. The cheek-piece bears two setae on its ventral surface, C 3 a large stiff 
seta arising from a conspicuous pit near the mid-ventral line, and C 4, shorter 
and finer, arising close to the lateral margin of the cheek-piece near its ex¬ 
tremity. 
Between the cheek-pieces on the ventral surface is a complex structure 
which I prefer to call the lower lip ( ll ). It is the homologue of what is 
called the hypostome in ticks, but the term is slightly ambiguous. In 
the Ixoidea it is defined as a “median ventral structure arising from the 
basis capituli” (Nuttall, Warburton, Cooper and Robinson, 1911, p. 127), but 
in the rest of the Acarina it is used (e.g. by Hirst) for a ventral structure com¬ 
parable to the epistome; in fact in this sense of the word the epistome and 
25 microns 
i--1 
Fig. 8 
Fig. 9 
Fig. 8. Sarcoptes scabiei var. equi. Dorsal aspect of lower lip of adult female, er, erect body; 
ll, lower lip; t, languette or tongue. 
Fig. 9. Left chelicera, lateral aspect. The dorsal side is to the left, bs, base of chelicera; cd, 
condyle; dg, digit; tb, tubercle of digit. 
hypostome are folds of the general body integument and lie respectively 
above and below the insertion of the basis capituli into the camerostome. The 
lower lip as I shall call this structure (Fig. 8), arises from the rounded knobs 
(kri) of chitin which as I have already said are formed by the union of the 
chitinous bands b 4 and b 5. It is a flat strip of chitin, for the most part thin 
and colourless, strengthened at its base by an acutely angled area of slightly 
thicker chitin. At each side of its extremity arises an erect body (er), which 
is immediately ventral to the chelicerae. These erect bodies are not articulated 
upon the extremity of the lower lip, but are simply continuations of its lateral 
margin; they are sharply excavated on their mesial aspects. Between these 
erect bodies the extremity of the lower lip is abruptly truncated. The tip of 
the structure known as the languette or tongue (t) lies upon the dorsal side 
