60 



COMPARATIVE ZOOLOGY. 



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 

 wx Insects, are developed into formidable 



FIG. 24. Mouth of the i i , i / , i 



liorse-fiyci'abamtsim- claws : both of these organs are prehen- 



eola): a, antennae; m, 

 mandibles; mm, max- 



T n 



o n 



mp, maxillary bles, which move more or less vertically. 



palpi; Ib, labrum; I, , . , , V 



labium, or tongue. end in a tang; and the club-like palpi, 

 often resembling legs, have 

 nothing to do with 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 . 25 ._ Under surTce of Male spider : , 

 ing with the water are con- C) P oison - fan g ; & teeth interior mar- 



gin of mandible, e; /, hibium; g, thorax; 



(Fig. 279). h, limbs ; ?; abdomen ; I, spinnerets ; m, 



mi ,1 ,. Tr maxillary palpus; d, dilated terminal 



ine mouth 01 Verte- joint. 



