The External Anatomy of Spiders 



Fig. 123. A TENENT HAIR FROM THE 

 EMPODIUM OF CLUBIONA 



The daws. — Each tarsus of the legs is armed with two or 

 three claws. When three claws are present, they can be desig- 

 nated as the paired daws and the third daw respectively. 



The paired daws are placed side by side at the tip of the 

 upper surface of the tarsus, or of the praetarsus if it is distinct; 

 they are usually armed with a series of teeth (Fig. 121). 



The third claw is a modified empodium (see below); when 

 present, it is situated below the paired claws. It is smaller than 



the paired claws, and 

 is sometimes armed 

 with a small number 

 of fine teeth. Usually 

 the terminal portion 

 is bent down rather 

 abruptly (Fig. 121). 



The empodium (em- 

 po'di-um). — When 

 the terminal portion 

 on the middle line of the praetarsus projects between or below 

 the paired claws it is termed an empodium. Sometimes the em- 

 podium is claw-like; it then constitutes the third claw described 

 above; sometimes it is a cushion-like pad or adhesive lobe; and 

 sometimes it is not devel- 

 oped as a distinct part. 

 Many terms have been 

 applied to this part; among 

 them a.rearolium,onychium, 

 palmula, plantula and pul- 

 villus. 



The accessory daws. — 

 In many spiders, especially 

 those that spin webs, the 

 tip of the tarsus is armed 

 with several claw-like 

 opines; these have been 



termed the accessory daws (Fig. 122). The accessory claws are 

 very different morphologically from the true claws, being modified 

 hairs each produced by a trichogen; while the true claws are 

 spine-like projections of the body-wall formed by many hypo- 

 dermal cells. 



Fig. 124. TIP OF TARSUS OF CLUBIONA 

 WITH TERMINAL TENENT HAIRS 



124 



