HOW ANIMALS EAT 



26l 



As most of the arachnids live by suction, the jaws 

 are seldom used for mastication. In the scorpion, the 

 apparent representatives of the mandibles of an insect 

 are transformed into a pair of small forceps, and the 

 palpi, so small in insects, are developed into formidable 

 claws : both of these or- 

 gans are prehensile. In 

 spiders, the so-called man- 

 dibles, which move more 

 or less vertically, end in 



FIG. 222. Mouth of the Horsefly ( Taba- 

 nus lineola), magnified: a, antennae; 

 nt, mandibles; tnx, maxillae; mp, 

 maxillary palpi ; Ib, labrum; /, labium, 

 or " tongue." 



a fang; and the clublike 

 palpi, often resembling 

 legs, have nothing to do 

 with ingestion or locomo- 

 tion. Both scorpions and 



spiders have a soft upper FlG - 223 ' - Under Surface of Male s P ider ' 

 lip, and a groove within 

 the mouth, which serves 

 as a canal while sucking 

 their prey. The tongue is external, and situated be- 

 tween a pair of diminutive maxillae. 



In the ascidians the first part of the alimentary canal 

 is enormously enlarged and modified to serve as a gill 

 sac. At the bottom of this sac, and far removed from 



enlarged: a, c, poison fang; b, teeth on in- 

 terior margin of mandible, e ; f, labium ; g, 

 thorax; h, limbs; i, abdomen; /.spinnerets; 

 m, maxillary palpus; d, dilated terminal 

 joint. 



