60 



COMPARATIVE ZOOLOGY. 



FIG. 94. Mouth of the 

 Horse-fly (7'<6an!wttn- 

 eola): a, antennas; m, 

 mandibles; mx, max- 

 illse ; mp, maxillary 

 pnlpi; Ib, labrnm; I, 

 labiura, 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 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- F .o.S5._Under Surf,, CB of Male Spider :, 



ing with the water are con- c - P"i*"-fc"s b - '<*'" <>,, interior mm- 



' gin of mandible, f; f, Inbtnm; g, thorax; 



(Fig. 279). A, limbs; i, abdomen; I, spinnerets; wt, 



r,-,, , . i T maxillary palpus; d, dilated terminal 



The mouth of Yerte- joint. 



