230 



LECTURE XI. 



104 



Jaw and teeth. 

 Leech. 



medicinal leech {Sanguisuga) {fig. 102.), and of Hcemopis, is tri- 

 angular, and is armed with three crescentic jaws 

 (a, a, a), presenting their sharp convex margin to- 

 wards the oral cavity, which margin is beset with 

 sixty small teeth {fig. 103.). It is by the action of 

 these little saws upon the tense in- 

 tegument seized by the labial sucker, 

 that the characteristic triradiate bite of 

 the leech is made. 



The oesophagus {fig. 104. b) is short, 

 and terminates in a singularly compli- 

 cated stomach, divided by deep con- 

 strictions into eleven compartments, 

 the sides of which are produced into 

 C£ecal processes {c, c'), progressively, 

 though slightly, increasing in length to the tenth, and 

 disproportionately elongated in the eleventh compart- 

 ment. The first gastric chamber is the smallest. In 

 the eight postei'ior compartments the anterior part of 

 frf'^ each slightly expands to form a pair of small acces- 



■■"^ - sory cceca. The middle part of the eleventh division 



extends backwards, in the form of a small funnel- 

 shaped process, and opens into the commencement of 

 the slender intestinal canal {d, d) ; this is situated be- 

 tween the two last and longest gastric caeca (c^) ; it 

 terminates by a small anus (e) above the terminal 

 sucker.* This is the position of the vent in most 

 Suctoria ; but some sea-leeches {Piscicola) offer an 

 exception in the ventral position of the outlet upon the 

 last segment. 



The modifications of the alimentary canal itself in 

 other genera are considerable. In Nephelis it is a 

 simple tube, gradually expanding towards the vent ; in 

 Branchiobdella the canal presents many circular con- 

 in Pontohdella it gives off a single pair of caeca near its 

 hinder third ; Hcemopis and Clepsi?ie present the same multiccecal 

 type of the canal as that which has been described and figured in 

 Scmguisvga. 



There is a stratum of round whitish glandular corpuscles, beneath 

 the coats of the pharynx and cesophagus of the medicinal leech, which 

 represents the salivary system. A peculiar brown tissue extends 



L^ech. 



strictions 



* See Preps. Nos. 442. 46C, 467, 468. 569. 595. A, 



