372 



COLLEGE ZOOLOGY 



There are six pairs of appendages attached to the cephalo- 

 thorax. Antennae are absent; their sensory functions are in part 

 performed by the walking legs. The first pair of appendages are 

 called chelicera (Fig. 314, ip). They are in many species com- 

 posed of two parts, a basal "mandible" (Fig. 313, B), and a 

 terminal claw. Poison-glands (Fig. 314, 20) are situated in the 

 chelicerae. The poison they secrete passes through a duct and 



out of the end of the chelicera 

 (Fig. 314, ip); it is strong 

 enough to kill insects and to 

 injure larger animals. The 

 second pair of appendages are 

 the pedipalpi (Fig. 313, palpus 

 and maxilla) ; their bases, 

 called " maxillae," are used as 

 jaws to press or chew the 

 food. The pedipalpi of the 

 male are used as copulatory 

 organs. 



Following the pedipalpi are 

 four pairs of walking legs. This 

 number easily distinguishes 



FIG. 313. External features of a _* . 



spider. A, under surface; all but one spiders from insects, since the 



leg removed. B, front of head show- latter possess only t h ree pairs, 



ing eyes and mandibles. (rrom * 



Emerton.) Each leg consists of seven 



joints, - - (i) coxa, (2) tro- 



chanter, (3) femur, (4) patella, (5) tibia, (6) metatarsus, 

 (7) tarsus, and is terminated by two toothed claws (Fig. 315) 

 and often a pad of hairs (s) which enables the spider to run 

 on ceilings and walls. The bases of certain of the legs some- 

 times serve as jaws. 



The sternum lies between the legs, and a " labium " is situated 

 between the " maxillae." The eyes, usually eight in number, 

 are on the front of the head (Fig. 313, B). The mouth (Fig. 314, 

 j) is a minute opening between the bases of the pedipalpi (max- 



