Beneath the second abdominal segments are borne the “pectines” or comb-like organs. In their structure four portions are distinguishable, an anterior lamella or shaft attaching them to the body, a middle lamella, the teeth, and the fulcra, a series of small chitinous pieces intercalated between the bases of the movable teeth. 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. [Illustration: FIG. 170.—=A=, Diagram of a Scorpion’s leg; 1, coxa; 2, trochanter; 3, femur; 4, patella; 5, tibia; 6, protarsus; 7, tarsus; _p.s_, pedal spur; _t.s_, tibial spur. =B=, Fourth tarsus of _Palamnaeus swammerdami_; _l_, lateral lobe. (After Pocock.) ] =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 projection 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 small 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, unfortunately, authors are not agreed upon the nomenclature of the joints. Kraepelin[242] names them coxa, trochanter, femur, tibia, and three-jointed tarsus, and Simon[243] agrees with him. Pocock’s names[244] are coxa, trochanter, femur, patella, tibia, protarsus, and tarsus, and it is certainly