458 



ZOOLOGY. 



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, 

 however, are parasites. In the first, the mouth (Fig. 498) 

 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 pediforin, 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. 



ca t ce b ma m y 



Fig. 497. Nervous System, &c.* 



The moveable hook or claw of the mandibles has near its 

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

 tory canal of the venomous gland already spoken of, and the 

 liquid which it pours into the bottom of the wound causes 

 immediately the benumbing of the insects which these ani- 

 mals pursue, but is too feeble to injure man, and it is without 

 any reason that the common people often ascribe to the bite 

 of spiders the pimples and red spots which sometimes appear 

 on the skin. 



* Section of the cephalothorax of the Mygale (crab spider) , showing the 

 disposition of the nervous system : ct , cephalothorax ; m, mandible ; g, claw 

 or moveable hook terminating it ; 6, 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. 



