GENERAL CLASSIFK'ATIUX AND STliUCTURE. 



25 



clares tliat the first leg is tlie 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 ])y the sign of equality ; thus, 

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

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

 tirst })air 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 u]:)on 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 wliicli unites the leg to the body. 

 It is partly concealed beneath the cephalothorax, and 

 sometimes carries short, pointed processes. Second, the 

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

 the articulation of the leg u})on 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 (tb), whose length 

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

 the metatarsus (mtr), the penultimate joint, which a})- 

 proaches the length of tlie femur, is commonly longer 

 than the 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 witli a great nund)er of spines, bristles, 

 and hairs, which are placed more freely along the inner surfaces 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 si)inning the snare. 



Orbweavers have three strong, genuine claws u})()n tluir tarsi, of whicli 

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

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

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

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

 near the l)ase. The extremity of the tarsus is always provided with two 

 or more auxiliaiy claws (au.cl).- One of these, a strong spiiir, lias the 



>cl ■ au.rl 

 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 

 Cla"ws. 



' 1 ]\;\\\' taken this fni-iniila as nnirc (•(iiuciiiciit foi- cxin'cssioti in \y\>r. 

 tlio rijiial iiirmlK'rH are joined liy a liracket ali<ivc. tlnis: 1 "_' 4 3. 

 - Thorell, Eumiiean SjjiiU'i-s, pau'e 47. 



In most nutlioi'S 



