112 ANIMALIA ARTICULATA. 



it returns, as venous blood, through the vessels E, into the 

 dorsal vessel, which transmits it into the vessel C, where, 

 after having regained its nutritive properties, it returns, by 

 the vessels F, into the dorsal vessel, and there mixes with the 

 venous blood brought by the vessels E. 



FAMILY II. ABRANCHIATE ASETIGERE. 



One remarkable genus. 



HIRUDO, Lin. Leech. 



Body elongated, flat beneath, convex above, soft, retractile, 

 and composed of a great number of segments ; small aper- 

 tures are to be observed in the inferior surface and upon the 

 sides, corresponding to small vesicles, considered by some 

 authors as organs of respiration ; mouth sometimes composed 

 (as in the medicinal species) of a vent-hole, encircled by a 

 lip, at the bottom of which are three jaws, each armed upon 

 the edge with two rows of very fine teeth ; sometimes the 

 teeth are few and blunt ; sometimes the mouth is entirely 

 without horny points; crawling is effected by means of the 

 disk at the mouth, and another placed at the posterior part 

 of the body. 



Pulmonary circulation of the Leech, PL 31, Fig. 2 : A, a 

 lateral vessel; B, pulmonary auricle; C, latero-dorsal vessel; 

 D, a latero-abdominal vessel; E, pulmonary vessel ; F, pul- 

 monary pouch. 



In the Leech there are four longitudinal trunks, one of 

 which is the dorsal vessel, another the subnervous, and the 

 other two are abdominal vessels. These vessels all commu- 

 nicate with each other both by capillaries and by large 

 branches (C, D). From these branches are given off the 

 vessels destined for general nutrition and cutaneous respira- 

 tion ; but there is likewise a pulmonary respiration carried 

 on by means of a double apparatus, consisting of particular 

 vessels and a pulmonary pouch (F). The blood passes from 

 the vessel D through E into the capillaries on the surface of 

 the pouch F ; it returns from thence through the pulmonary 

 auricle B into the lateral vessel A. 



