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THE CAPITULUM OF PSOROPTES (ACARINA) 1 . 
By P. A. BUXTON, M.A., 
Fellow of Trinity College , Cambridge. 
(From the Quick Laboratory, University of Cambridge.) 
(With 2 Text-figures.) 
This short account of the capitulum and mouth-parts of Psoroptes has been 
prepared as a preliminary to investigations which are being made upon the 
bionomics of the Itch Mites. None of the published figures or descriptions 
are complete. The best is that of Megnin. 
The general appearance of the capitulum can be seen from Fig. 1, A and B. 
Viewed as a whole it is roughly pear-shaped and is inserted into the front part 
of the body. The dorsal surface (Fig. 1 B) is overhung by a fold of the general 
integument (d.f., the dorsal fold or epistome), the ventral surface is free, except 
where it joins the body proximally. The basis capituli ( b.c.) bears two pairs 
of setae on its ventral surface, a short pair arising near the palpal articulation 2 
(si) and a longer pair situated closer to the mid-ventral line. The base of the 
palp is so shaped ventrally that it very nearly surrounds the origin of $1. 
Both pairs of setae are directed downwards and forwards. Between the bases 
of the second pair (s2) the surface of the basis capituli bears a minute keel¬ 
like structure (k) which protrudes strongly in front. The distribution of the 
sculpturing on the ventral surface of the basis capituli is shown in Fig. 1 A. 
There is a roughly rectangular bare area (b.a.) near the insertion of the basis 
capituli into the body, and the sculpturing does not extend quite as far forward 
as the point of origin of the second seta; there is no sculpturing on the dorsal 
surface of the basis capituli, nor does it extend far up the side. 
The mouth-parts themselves are shown in Fig. 2. I can find no difference 
between those of the male and of the female. The chelicerae (Fig. 2 C) are long 
and finely chelate. Each of the limbs which form the chela is armed with 
two recurved hooks ( h ), curved ventrally. The base of the chelicera is wider 
and more thickly chitinized than the extremity, and extends back inside the 
capitulum to a point slightly behind the origin of seta 2. In the dead mite 
1 Work carried out with the aid of a grant from the Ministry of Agriculture and Fisheries. 
2 I refer to the second appendage of Psoroptes as palp in accordance with the usage of most 
of those who have studied the Ticks and Mites. On strict morphological grounds it should be 
called a “pedipalp,” the name which is used for the second appendage of Arachnoidea in general. 
