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240 Ill. PROLES ARACHNES<br />
29. THE ORDER SOLIFUGAE 241<br />
diameter carries setae 3 cm long. It is said that if the tip of but a single<br />
seta be touched even with a hair, the animal responds instantaneously.<br />
The opisthosoma of Solifugae is always a regular oval, the posterior<br />
margin being a smooth curve with no trace of a post-anal structure. It is<br />
always conspicuously and completely segmented, and the somites<br />
carry both tergites and sternites. The number of somites appears to he<br />
ten, but 11 are present in the embryo, and this number is really retained<br />
in the adult, the first somite being much reduced. Its sternite<br />
is a small triangular plate between the fourth coxae, and its tergite is<br />
similar in shape and lies hidden between the prosoma and the opisthosoma.<br />
The genital orifice on the second sternite is a slit-like aperture<br />
peculiar among <strong>Arachnida</strong> in being guarded by movable lips, so that<br />
it can open and close. The third, fourth and fifth sternites show just<br />
behind their posterior edges the orifices of the opisthosomatic tracheae.<br />
There is a pair of these behind the third and the fourth sternites and a<br />
single, median one behind the fifth.<br />
DISTRIBUTION<br />
Solifugae are confined mainly to the tropical and sub-tropical regions,<br />
and in Europe occur only in the south-east of Spain (Fig. 105). The<br />
distribution of the separate families may be summarized thus:<br />
FAMILY<br />
DISTRIBUTION<br />
Fw. 104. Solifugae; ventral aspect.<br />
Galeodes arabs.<br />
differ from that of all others. The first pair of are much reduced<br />
and bear only three racket-organs each. Since the young of other<br />
families possess three such organs, this suggests that the Hexisopodidae<br />
exhibit neoteny. They and the family Rhagodidae have legs that are<br />
better adapted to digging than the legs in other families. The legs in all<br />
the Solifugae bear spines or setae of every degree of stoutness from short<br />
sharp spikes to long hair-like setae. There is not much evidence of<br />
thinking that any of these have any other function than that of organs<br />
of touch, as in all the orders of the <strong>Arachnida</strong>, but in Solifugae they<br />
seem to be more plentiful and more sensitive than in their allies. No<br />
other arachnid is so ''hairy" that to a casual glance it looks like a ball of<br />
fluff, and no other can show such proportions as those found, for examplc,<br />
in the fourth leg of the male Solpuga monteiroi, where a leg 2 mm in<br />
Melanoblossiidae<br />
Eremobatidae<br />
Karschiidae<br />
Rhagodidae<br />
Hexisopodidae<br />
Gylippidae<br />
Solpugidae<br />
Ammotrechidae<br />
Galeodidae<br />
Ceromidae<br />
Amacataidae<br />
Dacsiidae<br />
South-East<br />
?\ortb and Central America<br />
Asia; l'\ car East; north -west Africa<br />
north-east Africa; Near East; south-west Africa<br />
South Africa<br />
East Asia<br />
Africa<br />
South and Central America; southern North America<br />
Asia; North Africa<br />
South Africa<br />
western South America<br />
Near East; Africa; 1\:feditcrrancan zone<br />
The above table may be expanded thus. Solifugae occur over almost<br />
the whole of Africa. In Asia they are to be found in Arabia, Persia,<br />
Turkestan and India. They also occur in Celebes and Indo-China. The<br />
:r\ ear East species extend as far west as the coast of Palestine and as far<br />
north as the Caspian Sea.<br />
American Solifugae fully studied by M. H. Muma belong to the<br />
families Eremobatidae and Ammotrechidae. They are now known from
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