60 



COMPARATIVE ZOOLOGY. 



'772X 



Fig. 24.— Mouth of the 

 Horse-fly (Tabanus lin- 

 eola) : a, antennae ; m, 

 mandibles; mx, max- 

 illae; mp, maxillary 

 palpi; lb, labrum; 7, 

 labium, or tongue. 



As most of the Arachnids live by suc- 

 tion, the jaws are seldom used for masti- 

 cation. 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 organs are prehen- 

 sile. In Spiders, the so-called mandi- 

 bles, which move more or less vertically, 

 end in a fang; and the club-like palpi, 

 often resembling legs, have 

 nothing to do w T ith inges- 

 tion or locomotion. Both 

 Scorpions and Spiders have 

 a soft upper lip, and a 

 groove within the mouth, 

 which serves as a canal 

 while sucking their prey. 

 The tongue is external, and 

 situated between 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 

 its external opening, lies 

 the entrance to the diges- 

 tive tract proper. Into it 



the particles Of food enter- FlG . 2 5.-Under Surface of Male Spider: a, 



in£ with the water are con- Cj p° isou - fan s ; & > teet » <>» interior mar- 



° # gin of mandible, e; /, labium; g, thorax; 



Veyed (Fig. 279). h limbs; i, abdomen; Z, spinnerets; m, 



, n -r-r- maxillary palpus; dilated terminal 



I he mouth of Verte- joint. 



