Savory - Arachnida 1977

222 Ill. PROLES ARACHNES
posterior pair backward and somewhat upward. But false scorpions are
not animals whose lives are much governed by the sense of sight; they
are almost wholly dependent on touch.
In front of the carapace the chelicerae articulate. These are pre-oral
appendages of two joints, specialized for four functions (Figs 91 and 92).
Their most obvious use is comparable to that of the human hand-they
hold the food which the animal is eating, and they pick up and carry
food particles and also the grains of sand used in nest-making. They are
spinning organs, bearing on the tip of the movable finger a galea or
spinneret from which the silk issues. It is to this presence of a silk gland
in the chelicerae that the false scorpions owe the name of Chelonethi,
given them by Thorell. Thirdly, the chelicerae are bearers of sense
organs in the form of setae and lyrifissures; and no doubt this variety of
functions is the cause of the frequent cleaning of the chelicerae which
the animals carry out when they preen.
28. THE ORDER PSEUDOSCORPIONES 223
ii- --
iii---
---- -iv
---v
--vi
--vii
FIG. 91. Chelicera of a pseudoscorpion. After Chamberlin. (i) Flagellum; (ii) serrula
exterior; (iii) galea; (iv) galea! seta; (v) lamina! seta; (vi) lamina interior; (vii)
lamina exterior.
FIG. 92. Chelicera of Obisiwn simile. After Schenkel.
The chelicerae of Pseudoscorpiones are variable in size but constant
in proportions throughout the order.
They may, as in the Feaellidae, be so small as scarcely to project
beyond the edge of the cucullus, or they may be almost as long as the
cephalothorax, as in the Chthoniidae. The first segment has a broad base
or palm, prolonged into a pointed fixed finger. The second joint or
movable finger articulates ventrally and moves up and down not quite
vertically below the fixed finger. Upon the inner edge of each finger is
a comb-like lamina or serrula. These arc the active agents in the grooming
of the pedipalpi, which are drawn through the "jaws" and so over
the serrulae. \Vhen the chelicerae are large their tips generally cross
when the m ova blc finger is closed, the serrulae are attached to the
fingers only for part of their lengths, and the galea is usually small or
absent. This condition essentially fits the chelicerae to function as
grasping organs. When the chelicerae are small, they are not so efficient
for grasping. The finger-tips do not cross, but their tips fit into each
other, the serrulae are attached throughout their whole length and the
galea is usually well-developed. The earlier methods of classifying the
order of Chelonethi were based on these differences. The spinneret or
galea is always situated on the outer side of the tip of the movable
finger. It is of two types, a short chitinous tubercle or a slender, translucent
and often branched tube.
The silk glands with which it is in communication are of special
interest, because they occupy the same position as the venom glands of
many spiders. That two apparently similar glands should produce