4G8 



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.ef> 



I m. 



cm. 



It, 



nst n.s vs n 



FIG. 371. II irudo medicinalis ; Transverse section, b. t. botryoidal tissue ; c. id. circular 

 muscles; cr. crop; cr'. diverticula of crop ; cc. cuticle; /I. cp. epidermis; <l. s. dorsal sinus ; 

 d. v. m. dorsal-ventral muscles; 1. in. longitudinal muscles; I. c. lateral vessel; n. c. nerve- 

 cord ; nph. 1 It, nephridium ; n. s. nephrostomial sin-us ; nst. nephrostome ; is. testis ; r. it. 

 vas defereiis ; rs, vesicle of nephridium ; v. 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 jcwus, 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 

 l>li<ii'i/nx (Figs. 373 and 374, ph.} situated 

 in the fourth to the seventh segments. 



FIG. 372. one of the jaws of 



