xii 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 nf 

 six joints. The coxa is small and has an inwardly directed 

 lamella which assists in feeding. The trochanter is also a small 

 joint, bearing, normally at right angles to the longitudinal axis, 

 the powerful humerus or femur. Then follows the hraeliiuin 

 or tibia, again directed forward, and the last two joints form the 

 ehela or " hand," the terminal joint or movable linger hem- on 

 the outer side as in the chelicerae. In systematic determination 

 special attention is given to the "hand." In some furms the 

 upper surface is uniformly rounded, while in others a finger- 

 keel" divides it into two Hattish surfaces almost at riidil angles. 

 The biting edges of the fingers are usually furnished \\iih rows 

 of minute teeth arranged characteristically in the din'rivnt 

 genera. The ambulatory legs are seven-jointed, though, unfor 

 tunately, authors are not agreed upon the nomenclature of the 

 joints. Kraepelin ' names them coxa, t n.ehanter, fnnur, t ibia. and 

 three-jointed tarsus, and Simon " agrees wit h him. Pococls names 



1 Das Tierreich, 8. Lief., I 1 - 1 .' 1 .'. |>. 1. 

 - . triii -Imiili 'X ili l-'i-n iii-i\ vii., 1*7'.'. i' 

 3 nf Jlr/i/.i/i Jin/i". " Ai-Mi'liiiid.-i," 1 !'<)(). ].. s. 



