OF THE CLASS ABACHNIDA. 415 



same; the anterior ganglions (c), situated in front of and 

 above the gullet, and considered most generally as represent- 

 ing the brain of these animals, give origin to the optic nerves 

 anteriorly, and are continuous behind with the oesophageal 

 collar ; the other ganglions are situated under the alimentary 

 tube, and send nerves to the limbs, abdomen, &c. 



555, The arachnida are carnivorous, but confine them- 

 selves generally to suck the humours contained in the dead 

 body of their victim ; and in order to render easy the capture 

 of animals whose strength they might dread, nature has pro- 

 vided a great many of them with a venomous apparatus. 

 Most of them feed on insects, which they seize alive ; some 



Fig. 411. Xervous System, &c.* 



however are parasites. In the first, the mouth (Fig. 412) 

 is furnished with a pair of mandibles, armed with move- 

 able hooks, or formed like forceps of a pair of lamellated 

 jaws, having each a large feeler more or less pediform, and 

 some of a lower lip ; in the parasite arachnida, the mouth has 

 the form of a small proboscis, whence springs a kind of lancet 

 formed by the jaws. 



The moveable hook or claw of the mandibles has near its 

 extremity a small opening, which is the orifice of the excre- 



* Section of the cephalothorax of the Mygale, showing the disposition of 

 the nervous system : ct, cephalothorax ; m, mandible ; g, claw or moTeable 

 hook terminating it ; b, mouth ; ce, the gullet ; e, the stomach ; ab, origin 

 of the abdomen ; c, brain or cephalic ganglion ; t, ganglionary mass of the 

 thorax; ca, cords uniting the abdominal ganglions; no, optic nerve ; y, the 

 eyes. 



