128 
Sarcoptes 
of the extremity of the lower lip, and may be seen projecting over its truncated 
margin. The appearance of the languette from above is seen in* Fig. 8. It is 
a flat oval piece of chitin, deeply incised at the base, and thickened by a chi- 
tinous median ridge. It is analogous, if not homologous, to the hypopharvnx 
of insects. 
The palp (pp) (morphologically the pedipalp) is an organ lying on each 
side of the capitulum above the cheek-piece, below and to the side of the 
chelicera. In general shape it is cultriform, and when the two palps are flexed 
their terminal joints meet across the chelicerae. The palp is articulated to the 
base of the basis capituli over a wide area along the line of the chitinous band 
b 4; it consists of three joints, and the lines dividing them from one another 
are more clearly marked below than above. The first joint must be nearly 
immoveable, by reason of its articulation over a wide base to the basis capituli, 
and of its position between the chelicera above and the cheek-piece below; it 
is greater in length than the second and third joints combined, and is devoid 
of setae. The second joint bears the first capitular seta (C 1) on its dorsal 
surface; the third joint which is the shortest of the three and triangular in 
shape, bears the seta C 2 on its dorsal surface. The third joint terminates in a 
blunt point, without any of the delicate finger-like processes found in the 
closely allied Psoroptes (Buxton, 1920). 
The chelicerae (Fig. 9) lie on the dorsal side of the capitulum, and are 
exposed for the greater part of their length. They lie above the palp and close 
to the middle line. Their general shape can be seen from Fig. 9. The chelicera 
is short; thick, slightly concave downwards and convex upwards. It consists 
of two portions, a base (bs) and a digit (dg). The base which forms the main 
part of the chelicera, bears a rounded articular surface or condyle (cd), which 
is in contact with a conspicuous articular surface inside the basis capituli. 
At its extremity it is decurved so as to form the upper limb of a chela, and it 
bears three teeth. To the mesio-inferior aspect of the base is articulated the 
digit (dg), which is not toothed but can be brought into opposition with the 
toothed extremity of the base; this completes the chela. All previous authors, 
except Bobin, who give any attention to the matter figure and describe the 
digit as toothed. This is I believe due to an optical illusion; the whole chelicera 
is very small and when the chela is closed the teeth at the extremity of the 
base overlap the margin of the digit and impart to it a toothed appearance. 
The two parts of the chelicera are so jointed together that the tubercle of the 
digit lies free in the interior of the base. A muscle inserted on the tubercle and 
arising from the apodeme in the ventral side of the base would close the 
chela by bringing the two portions together. I have never been able to see 
such a muscle either in Sarcoptes or in Psoroptes in which genus I have recently 
figured a similar disposition of tubercle and apodeme. 
So much for the description of the capitulum. There remain to be con¬ 
sidered certain discrepancies between my interpretation and those of earlier 
writers. 
