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126 III. PROLES ARACHNES<br />
14. THE ORDER PALPIGRADI 127<br />
FIG. 34. Komenia<br />
lateral aspect. After Kraepelin.<br />
Fm. 33. Palpigradi; dorsal aspect. Species, Koenenia mirabilis.<br />
are chelate, the pincers working laterally. They are the only<br />
chelate limbs of Palpigradi and their only weapons; they are consequently<br />
capable of very free movement, and, with their long proximal<br />
have a comparatively wide range (Fig. 34).<br />
The pedipalpi are simple pedal structures, not specialized for any<br />
particular function and used in so leg-like a manner that, if the first pair<br />
of legs were used normally, Palpigradi might be said to possess five pairs<br />
of walking legs. The pedipalpi consist of nine podomeres, the tibia being<br />
followed by a basitarsus of two parts, while the tarsus is divided into<br />
three. There is a pair of terminal cla,vs.<br />
The first pair of true legs are by far the longest of the appendages,<br />
with a basitarsus (metatarsus) in four parts and a tarsus in three, it<br />
totals 12 pieces. The last six of these carry long sensory setae. The<br />
limb is not used for walking, but is carried stretched out ahead of the<br />
animal, in the same way as are the forelegs of some of the spiders and<br />
mites. It is clear that these legs are the chief sense organs of the animal.<br />
·The second and third legs have the normal complement of seven segments<br />
each, but the fourth, owing to the of a divided tarsus,<br />
number eight segments. All the legs have two claws on the tarsi.<br />
The mouth of Palpigradi is unique. Belo·w the proximal end of the<br />
chelicerae is a soft egg-shaped prominence, pointing forward and composed<br />
of epistome and hypostome. The mouth appears as a transverse<br />
slit at the end of this oral process, lying as it were between the two lips.<br />
There is no other arachnid in which the mouth is so far forward as to<br />
lie between the basal joints of the chelicerae, and it may be that this is a<br />
primitive position, from which the mouth has not migrated as far back<br />
as it has in the allied orders.<br />
The sternum is also very remarkable, differing from that of all other<br />
<strong>Arachnida</strong> and probably representing a much more primith·e<br />
There are four pro somatic sternitcs (Fig. 35). The anterior of these is<br />
the largest and consists of the fused sternites of the segments the<br />
pedipalpi and the first pair oflegs; the three succeeding ones arc smaller<br />
and lie directly between their corresponding conical coxae. Thus if<br />
the hypostome be taken as representing sternite 1, the large anterior<br />
plate represents sternites 2 and 3, and the remainder sternitcs 4, 5<br />
and6. This is a full complement and there is no other arachnid prosoma<br />
with so well-defined a segmentation on its ventral surface.<br />
A soft weakly-sclerotizcd pedicel unites the two parts of the<br />
body, and is followed by an opisthosoma of 11 more somites. Tergites<br />
and stcrnites, though present, are weak and transparent; they are<br />
visible in ordinary circumstances, but can with some difficulty<br />
be seen with the help of a microscope. The genital orifice lies on
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