468 



ZOOLOGY 



SECT. 



fibres. There are also dorso-ventral fibres (d. v. m.) passing vertically 

 between the pouches of the crop (vide infra), and radial fibres ex- 



d.s 

 i-m, 



.d.v.m. 



b.t 



njbh 



v.d 



nat n.s vs ' 



t *-.& 



FIG. 371. HirudO medicinalis ; Transverse section. 1. t. botryoidal tissue ; c. m. circular 

 muscles ; cr. crop ; cr'. diverticula of crop ; cu. cuticle ; d. ep. epidermis ; d. s. dorsal sinus ; 

 d. v. m. dorsal- ventral muscles ; I. m. longitudinal muscles ; I. r. lateral vessel ; n. c. nerve- 

 cord ; nph. 1 A, nephridium ; n. s. nephrostomial sinus ; nst. iiephrostome ; ts. testis ; r. d. 

 vas deferens ; vs, vesicle of nephridium ; r. s. ventral sinus. (After Marshall and Hurst.) 



tending from the wall of the enteric canal to the integument : 



these take the place of the septa of Chsetopods. 



The alimentary organs are greatly modified in accordance 



with the blood-sucking habits of the animal. Surrounding the 

 mouth are three jaws, one median and 

 dorsal (Fig. 374, d. /.), the other two 

 ventro-lateral (v. /./.). Each (Fig. 372) 

 has the form of a compressed muscular 

 cushion, with a sharp, evenly curved, free 

 edge covered with chitin, which is pro- 

 duced into numerous serrations or teeth : 

 by means of its muscles each jaw can 

 be moved backwards and forwards through 

 a certain arc, and the three, acting to- 

 gether, produce the characteristic triradi- 

 ate bite in the skin of the animal upon 

 which the Leech preys. 



The mouth leads into a muscular 



FIG. 372. one of the jaws of pharynx (Figs. 373 arid 374, ph.) situated 

 (Af l te?L?uc?a e r?. lcinalis< in the fourth to the seventh segments. 



