Savory - Arachnida 1977

224 III. PROLES ARACHNES
secretions so different in fimction and chemical composition might well
suggest that they cannot be regarded as truly homologous, but their
homology is made probable by the peculiar chelicera! glands of spiders
of the genus Scytodes. These spiders capture their prey by a method
which it is hard to parallel among other Arachnida. Approaching to
within a few centimetres of their victims, they spit a mixture of silk and
venom over them, a mixture that comes from the composite glands in
the chelicerae.
Yet another important biological feature associated with the chelicerae
is the ftagellum, situated on the medio-ventral side, near the base
of the inner digital condyle, and consisting in general of a group of
specialized setae (Fig. 93). In more primitive families the number of
setae is greater than in the more specialized, and varies from 12, in
28. THE ORDER PSEUDOSCORPIONES 225
some of the Ch thoniidae, to one, in Geogarypinae. The individual setae
are blade-like structures, feathery or toothed in appearance.
The interest of the fiagellum lies partly in its function, which Vachon
has described. When the fluids of the food have been sucked into the
pharynx a solid residue remains on the labial setae; the chelicerae are
drawn in and then thrust out, the setae of the flagellum spear the
accumulation of debris and push it out between the coxae of the pedipalpi.
Further, a flagellum is found on the chelicerae of several other orders,
providing a good instance of comparative arachnology.
In Solifugae the ftagellum is limited to and is a mark of the male sex.
It is generally but a single structure but it shows specific differences and
is a valuable feature in classification (Figs 94 and 101). In the scorpions,
i
ii
FIG. 94. Flagellum of male Galeodes arabs. After Roewer.
FIG. 93. Chelicera! fiagella of Pseudoscorpiones. After Chamberlin. (i) Hya heterodonta;
(ii) Chthonius ischnocheles; (iii) Neobisium imperfectum; (iv) Atemnus oswaldi.
whose chelicerae are composed of three segments, the second segment is
coated with setae on its inner surface. None of these is developed conspicuously
into a ftagellum, but their existence in this position is
interesting, showing, perhaps, the primitive state from which the ftagellum
has been evolved.
In Araneae the proximal segment of the chelicerae is normally
unarmed, but there are certain species in which it carries a spine or
seta. The common British myrmecophile Phrurolithus Jestivus is the most
familiar: a strong spine directed fonvard rises from the anterior surface
of the paturon, quite close to the inner edge. Crosby (1934) has described
a two-eyed spider, lvfatta hambletoni, in which the chelicerae are
armed in front with a narrow short and blunt tooth (Fig. 95).
What appears to be the same thing is again to be found among the
Acari, where the chelicerae of mites belonging to the genus Parasitus
have a short spine at the base of the fixed finger (Fig. 96).
It must be admitted that there is at present no justification for the