XII EXTERNAL FEATURES et 7/ 
conceal the under surface of the caput. The shape of the 
sternum and of the labium, and the contour and degree of 
inclination towards one another of the maxillae, 
are important considerations in the taxonomy ep... 
of Spiders. 
WwW 
The appendages of the cephalothorax, which 
are the chelicerae or jaws, the pedipalpi or feelers, 
and the four pairs of ambulatory legs, will be 
treated separately. 
Pedicle.—The chitinous investment of the 
narrow stalk which unites the thorax with the 
abdomen is for the most part thin and flexible, 
with only slight indurations of various patterns Lilet 
on the dorsal surface, where it is in most cases ie banat 
more or less protected by the forwardly-projecting Se 
>> -a.b 
abdomen. Beneath, it is usually quite mem- , 
1G. 174.—Diagram- 
branous, guarded only by a sort of collar formed matic ventral view 
by the raised border of the anterior portion of See sy 
the abdomen at the point of insertion. In — Labium; m, max- 
some Spiders, however (Dysderidae), there is a Sane 
posterior sternal plate, the “plagula,’ closely — sternum; wu, un- 
corresponding with the labium in front, which ce ee 
partly embraces the pedicle. In Hermippus Anal tubercle; ¢, 
(Zodariidae) the plagula is detached from the a Ment 
sternum, and is succeeded posteriorly by two Be eee 
smaller paired plates. ing: 
Abdomen.— The abdomen differs remarkably 
in shape in the different groups of Spiders. In some families 
the prevailing shape is more or less globular, and in others 
cylindrical, while it may be diversified to almost any extent by 
prominences or spines. Ordinarily no sign of segmentation is 
observable, but in Liphistivs it is covered dorsally by seven 
well-marked chitinous plates. 
In most Spiders the integument of the abdomen is uniformly 
soft and flexible all over, but it is not rare to find portions of it 
thickened and hardened to form “scuta.” In the Gasteracan- 
thinae and the Phoroncidinae there is a great dorsal scutum 
armed with spines, while in several families there are species 
characterised by the possession of a smooth dorsal scutum ; and 
in some a ventral scutum is present. 
