GENERAL CLASSIFICATION AND STRUCTURE. 



25 



clares that the first leg is the longest, then the second leg, then the fourth 

 leg, and lastly the third leg. When two pairs of legs are of equal length 

 the numerals expressing them are united by the sign of equality ; thus, 

 12 = 43 indicates that the second and fourth legs ai'e of ec^ual length. ^ 

 For the most part the third leg is much the shortest of the four, and the 

 first pair decidedly the longest. This rule, however, varies in certain 

 genera, as Acrosoma, in which the fourth pair is as long as, or longer 

 than the first, a variation which seems to be adapted to the peculiar form 

 of the spider. The males have legs longer and slighter than the females, 

 and in some species have a special armature in the shape of a comb of 

 stout spines upon the tibia of the second pair, which probably serves as a 

 clasping organ in the act of pairing. 



The legs have seven joints, which are arranged in the following order, 

 counting from the point of union with the sternum : First, the coxa (ex, 

 Fig. 13), the short joint which unites the leg to the body. 

 It is partly concealed beneath the cephalothorax, and 

 sometimes carries short, jiointed processes. Second, the 

 trochanter (tch), a minute joint which really serves for 

 the articulation of the leg upon the body, the coxa being 

 fixed. Third, the femur (fm), usually the longest and 

 stoutest joint of all. Fourth, the patella (ptl), which 

 nearly corresponds in length with the coxa, and serves as 

 a sort of knee joint. Fifth, the tibia (tlj), whose length 

 is usually a little less than that of the femur. Sixth, 

 the metatarsus (mtrl, the penultimate joint, which ap- 

 proaches the length of the femur, is commonly longer 

 than tlie tibia, but much slighter. Seventh, the tarsus 

 (tr), the ultimate joint, which is usually shorter than the metatarsus. The 

 last five of these joints are armed with a great number of spines, bristles, 

 and hairs, which are placed more freely along the inner surface* of the 

 legs, and thus are disposed for the greatest advantage of the animal in 

 manipulating its prey, embracing its mate, or fighting its enemies. They 

 are also used in spinning the snare. 



Orbweavers have three strong, genuine claws upon their tarsi, of which 

 the two superior are pectinated, and (with rare exceptions) the inferior is 

 armed with two close and blunt comb teeth (cb.th). The supe- 

 rior claws are of equal size, placed side by side. The iirfcrior 

 claw is smaller than the others and is below them, bent down 

 near the base. The extremity of the tarsus is always provided with two 

 or more auxiliary claws (au.cl).^ One of these, a strong spine, has the 



i cl '••. au.cl 

 Fig. 14. Foot of Epeira 

 insularis. s.cl, superior 

 claw ; pc, pectinations 

 upon the superior claws; 

 i.cl, inferior claws ; au.cl 

 auxiliary claws upon the 

 tarsus. 



Tarsal 

 Claws. 



1 1 have taken this formula as more convenient for expression in type. In most authors 

 the equal members are joined 1 )y a liraeket above, thus : 1 2 4 3. 

 - Thorell, European Spidere, page 47. 



