ARANEWM. 



327 



anterior pair are much used as feelers. In the embryo there are four 

 pairs of abdominal appendages which abort. 



The nervous system is of the usual Arthropod type, but 

 shows much centralisation. Thus the ventral ganglia are 

 fused into one large centre 

 in the cephalothorax (see Fig. 

 141), a condition comparable 

 to that in crabs. There are 

 two or three rows of simple 

 eyes on the cephalothorax, 

 whose focal distance is very 

 short, spiders trusting most to 

 their exquisite sense of touch, 

 by which they discriminate the 

 various vibrations on a web 

 line. The senses of smell, 

 hearing, and taste are also pre- 

 sent, but little is known in re- 

 gard to the organs. 



Body cavity, endosternite, 

 and coxal glands generally re- 

 semble those of scorpions. 



The spider usually sucks the 

 blood and juices of its prey, 

 and behind the gullet lies a 

 powerfully suctorial region, 

 strengthened by 

 plates, and worked by muscles. 

 From the small mid-gut arise 

 five pairs of long caeca, a pair 

 running forwards and a pair 

 passing into the bases of each 

 pair of legs, and then back 

 again. These csca sometimes 

 anastomose. Further back the 

 mid-gut gives off numerous digestive outgrowths, which fill 

 a large part of the abdomen. Their secretion digests 

 proteids. Terminally there is a large cloaca, and where 

 the intestine joins this, four much-branched excretory 

 Malpighian tubes are given off, and are again said to be 

 endodermal in origin. 



rhirinniK; FlG - 141-— Dissection of Mygale 

 Ul from the ventral surface. —After 



Cuvier. 



:, Cheliceras ; 2, pedipalps cut short ; 

 3-6, walking legs ; g 1 . large thoracic 

 ganglion ; gK ganglion at base of 

 abdomen ; c.t., chambered tracheae 

 or lung-books — at the left side the 

 anterior is cut open to show the 

 lamellae (/.) ; m. , muscle of abdomen ; 

 st 1 . and sfi. t stigmata of lung-books ; 

 ov. , ovary ; sfi. , spinnerets. 



