230 



LECTURE XI. 



10-i 



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 

 cjecal 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 posterior compartments the anterior part of 

 each slightly expands to form a pair of small acces- 

 sory CEeca. 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) ofter 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 

 Brnnchiohdella the canal presents many circular con- 

 in Pontobdella it gives off a single pair of cajca near its 

 hinder third ; Hcemopis and Clepsine present the same multicascal 

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

 Sanguisiiga. 



There is a stratum of round whitish glandular corpuscles, beneath 

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

 represents the salivary system. A peculiar brown tissue extends- 



^l 



Leech. 



strictions 



* Sec Preps. Nos. 442. 46C, 4C7, 408. 569. 535. A. 



