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 

 A (JAL,r r J ^ our P a i rs f walking legs. This 



SPINNERETS 



FIG. 313. External features of a 

 spider. A, under surface; all but one 

 leg removed. B, front of head, show- 

 ing eyes and mandibles. (From 

 Emerton.) 



number easily distinguishes 

 spiders from insects, since tl\e 

 latter possess only three pairs. 

 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 " Idbium " 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, 

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



