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226 III. PROLES ARACHNES<br />
28. THE ORDER PSEUDOSCORPIONES 227<br />
FIG. 95. Left chelicera of Malta hambletoni, a Brazilian spider. After Crosby.<br />
Fw. 97. Pedipalp of Chthonius. After Beier.<br />
Fw. 96. Chelicera of the mite Parasitus, showing flagellum.<br />
assumption that all these chelicera! appendages are homologous,<br />
although from their situation it may well appear that they are. Nor can<br />
really be described as analogous, for their function is quite unknown.<br />
In Solifugae the fact that the ftagellum is confined to the male is<br />
crm,.~r·,.,p of a sexual fi.mction, but this has not been observed on the rare<br />
occasions when the mating of Solifugae has been witnessed. Lamoral<br />
( 1 that it acts as a store for an exocrine secretion, possibly<br />
functioning as a pheromone, which affects the female.<br />
The pedipalpi are organs which are of the greatest importance, not<br />
only as the principal weapons but also as the bearers of many tactile<br />
setae. also function in some species as secondary sexual organs.<br />
They arc invariably six-jointed and chelate (Fig. 97). The first segment<br />
or coxa is provided with a gnathobase or manducatory process and is<br />
often called the maxilla. It bears a pair of delicate lamellae, essential<br />
components of the mouth parts. The femur and tibia are the longest<br />
joints and can be bent to a very angle on each other. The metatarsus<br />
and tarsus compose the chela. The latter forms the movable<br />
finger and is articulated so as to work against the fixed finger<br />
above. It is opened by blood pressure and closed by a powerful adductor<br />
muscle which is spread within the swollen basal part of the m eta tarsus.<br />
The form of the pedipalp is very diverse; so great indeed is the variation<br />
that it is scarcely an exaggeration to say that it is different for every<br />
different species. There is generally a slight sexual dimorphism, the<br />
limb of the female being stouter than that of the male. The pedipalpi<br />
normally contain poison glands situated in the interior of the fingers<br />
with ducts opening at an orifice just below the tip of the last tooth. These<br />
glands may be in both fingers or in either finger only or be<br />
absent altogether as, for example, from the F eaellidae. Just posterior to<br />
the poison tooth or venedens a blade-like modified seta, the lamina<br />
defensor, is found. Its function is unknown.<br />
The metatarsus and tarsus together carry a number of tactile setae.<br />
These are long, simple and slender structures, each inserted at the<br />
bottom of a small depression. Ordinary "non-tactile" setae have not<br />
this depressed insertion. Typically each chela has 12 setae, though<br />
sometimes fewer and often more are present. The 12 are arranged<br />
in three series of four, one series on the exterior face of each finger and<br />
one on the inner face of the fixed finger.<br />
The eight legs are naturally divided into four pairs, for throughout<br />
the order the forwardly-directed first and second pairs are different<br />
from the backwardly-directed third and fourth pairs. Owing to this<br />
distinction, Kastner ( 1931) has called the former Zugbeine and the<br />
latter Shubbeine, but as pseudoscorpions often run backward the names<br />
are not altogether appropriate. The first always closely resembles the<br />
second, but the latter is slightly larger and the third is similar to but<br />
smaller than the fourth. The legs of the posterior pairs are usually the<br />
longest and stou test.<br />
The legs are typically composed of seven<br />
two of which<br />
compose the femur. There is no patella. An additional pretarsus,<br />
regarded by some as an eighth segment, is usually present. lVfodifications<br />
of this number of segments are found. Frequently the metatarsus
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