304 



ARACHNIDA — SCORPIONIDEA 



are coxa, trochanter, femur, patella, tibia, protarsus, and tarsus, and 

 it is certainly convenient that each joint should have a separate 

 name, but it must be borne in mind that the tibia of different 



authors is not always the 

 same joint. Special atten- 

 tion must be directed to 

 ^' ' ^ the three terminal joints, 



which furnish highly 



important characteristics. 



The tibia (in Pocock's 



"P'^ sense) is sometimes pro- 



/, ^ \ vided with a " tibial spur " 



at its lower distal ex- 

 tremity. From the soft 

 arthrodial membrane be- 

 tween the protarsus and 

 tarsus may proceed one 



Fig. 170.-A, Diagram of a Scorpion's leg; 1, ^^ more dark-tipped claw- 



coxa ; 2, trochanter ; 3, fennir ; 4, patella ; . ^ ^ 



5, tibia ; 6, protarsus ; 7, tarsus ; p.s, peilal like SpurS, the " pedal 



s^nr; t.s, tibial spur. B, Fourth tarsus of ^ >, r^^ve terminal 



Palamnaeus swammeraavn ; I, lateral lobe. ■■• 



(After Pocock.) joint (tarsus of Pocock) 



is variously furnished 

 wiih hairs and teeth, and always ends in a pair of well- 

 developed movable claws beneath which a much reduced and 

 sometimes almost obsolete third claw is distinguishable. The 

 tarsus generally projects in a " claw-lobe " over the base of the 

 superior claws, and sometimes lateral lobes are present. The 

 first and second coxae have triangular maxillary lobes directed 

 towards the mouth. The third and fourth coxae are fused 

 together on each side, and those on one side are separated 

 from those on the other liy the sternum. In other respects 

 the four pairs of legs are usually similar. 



Internal Anatomy. 



The alimentary canal is a fairly uniform tube, nowhere 

 greatly dilated. The very small mouth leads into a small 

 suctorial chamber, and this is connected by a narrow oesophagus, 

 which pierces the cerebral nerve-mass, with a slightly dilated 

 portion which receives the ducts of the first pair of gastric 



