XU SEGMENTATION—-APPENDAGES 303 
Beneath the third, fourth, fifth, and sixth segments are the 
paired openings of the lung-sacs. 
Metasoma.—The first segment is usually and the remainder 
are invariably enclosed in complete chitinous rings and show 
considerable variations in their comparative size and shape, and 
in the arrangement of the ridges and keels with which they are 
usually furnished. The post-anal segment is more or less 
globular at its base, constituting a “ vesicle,’ and terminates in 
a fine curved point, the “aculeus,” perforated for the passage of 
the delicate poison-duct. With the abdomen fully extended the 
point is directed downward, but in the attitude of attack or 
defence, when the “tail” is carried horizontally over the back, 
the sting points forward in the neighbourhood of the animal’s 
head. 
Appendages.—The three-jointed chelicerae are powerful and 
chelate. The first joint is small, but the second is strongly 
developed and bears at its anterior end on the inner side a_pro- 
jection which forms the immovable finger of the chela. The 
third joint, or movable finger, is articulated on the outer side, 
and both fingers are armed with teeth whose arrangement is 
useful in distinguishing the species. The pedipalpi consist of 
six joints. The coxa is small and has an inwardly directed 
lamella which assists in feeding. The trochanter is also a simall 
joint, bearing, normally at right angles to the longitudinal axis, 
the powerful humerus or femur. Then follows the brachium 
or tibia, again directed forward, and the last two joints form the 
chela or “hand,” the terminal joint or movable finger being on 
the outer side as in the chelicerae. In systematic determination 
special attention is given to the “hand.” In some forms the 
upper surface is uniformly rounded, while in others a “ finger- 
keel” divides it into two flattish surfaces almost at right angles. 
The biting edges of the fingers are usually furnished with rows 
of minute teeth arranged characteristically in the different 
genera. The ambulatory legs are seven-jointed, though, untor- 
tunately, authors are not agreed upon the nomenclature of the 
joints. Kraepelin } names them coxa, trochanter, femur, tibia, and 
three-jointed tarsus, and Simon * agrees with him. Pocock’s names ° 
1 Das Tierreich, 8. Lief., 1899, p. 4. 
2 Arachnides de France, vii., 1879, p. 84. 
3° Fauna of British India, ‘‘ Avachnida,’ 1900, p. 8. 
