XIL EXTERNAL STRUCTURE 309 
and South America. They are of ancient origin, a fossil genus, 
traecophonus, of the Tarantulidae (Phrynidae, see p.3 12), occurring 
in the Carboniferous strata in North America. They live under 
stones and bark, and in caves, where, when disturbed, they seek 
safety In crannies in the rock. 
Little is known of their habits, but they are believed to feed 
chiefly upon insects. The female 7arantula carries the developing 
egos, somewhat after the manner of the Chernetidea (see p. 454), 
in a bag beneath the abdomen, the under surface of which 
becomes concave and dome-like during the period of gestation.’ 
External Structure.— The external features which the 
members of this Order have in common are the segmented 
pediculate abdomen (9 to 12 segments), 
the two-joimted non-chelate chelicerae, 
the antenniform first pair of legs, and 
the presence of two pairs of lung-book 
stigmata beneath the abdomen. The 
constituent families differ so much in 
outward form that they must be dealt 
with separately. 
The Thelyphonidae or “ Whip Scor- 
pions ” (see p. 312) have a long-oval cara- 
pace bearing well-developed eyes, two in 
front, and a group of three or five on 
either side some distance behind. The 
pedipalpi are chelate, and have their basal 
joints fused beneath the mouth, being thus 
incapable of any masticating motion. 
The first legs are six-jointed, and pyg, 171.—Thelyphonus, dia- 
have multi-articulate tarsi; the others grammatic ventral view ; 
apis 5 ae about natural size. , 
are seven-jointed, and their tarsi, in some 
species at least, are tri-articulate. The 
abdomen consists of two portions, a wide 
nine-jointed pre-abdomen and a_ short 
narrow three-jointed post-abdomen, to 
which a filiform tail is articulated. 
Coxal joint of pedipalp ; 
g, generative opening ; 7, 
pedipalp ; sp, spiracles ; 
st, sternal plates; 1, 2, 3, 
4, ambulatory legs. (After 
Pickard-Cambridge. ) 
Beneath the cephalothorax, 
between the coxae of the legs, is a distinct sternal plate in two 
portions (Fig. 171). 
developed, and covers two segments. 
The first abdominal ventral plate is largely 
Behind it are the median 
1 Laurie, J. Linn. Soc. Zool. xxv., 1894, p. 30. 
