SPIDERS. 
the various vibrations on a web line. 
369 
The senses of smell, 
hearing, and taste are also present, but little is known in 
regard .to the organs. 
Body cavity, endosternite, and coxal glands generally 
resemble 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  chitinous 
plates, and worked by muscles. 
From the small mid-gut arise 
five pairs of long ceca, a pair 
running forwards and a pair 
passing into the bases of each - 
pair of legs, and then back 
again. These ceca sometimes 
anastomose. Farther back the 
mid-gut gives off numerous 
digestive outgrowths, which fill 
a large part of the abdomen. 
Their secretion digests pro- 
teids. Terminally there is a 
large cloaca, and where the 
intestine joins this, four much- 
branchedexcretory Malpighian 
tubes are given off, which are 
said to be endodermal in 
origin. 
A three-chambered heart, 
containing colourless blood, 
lies within a pericardium near 
the dorsal surface of the 
abdomen. It gives off an 
anterior and a posterior aorta 
and lateral vessels; and the 
Fic. 193.—Dissection. of AZygale 
from the ventral surface. —After 
Cuvier. 
1, Chelicerze; 2, pedipalps cut short ; 
3-6, walking legs; g.1, large thoracic 
ganglion; g.2, ganglion at base of 
abdomen; c.#., chambered trachez 
or lung-books—at the left side the 
anterior is cut open to show the 
lamellee (2.); 2., muscle of abdomen; 
stl and sz.2, stigmata of lung-books ; 
ov., ovary ; Sf., spinnerets. 
circulation corresponds in general to that of the scorpion. 
In a few forms (Tetrapneumones) respiration is effected 
by four “lung-books,” e.g. in the large bird-catching AZygale 
(Fig. 193). 
two lung-books, and tubular trachez in addition. 
24 
In the vast majority (Dipneumones) there are 
The 
