Medicinal Leech. 131 



opens as a nipple-shaped process^ into the bilohed commencement 

 of what Gratiolet calls the * gastroileal'' intestine, the mucous 

 membrane of which is prolonged into spirally-arranged valvulai 

 folds. This ' gastroileaF intestine ends in an ovoidal colon ; and 

 this again in a short rectum of very small calibre, which terminates 

 in a dorsally-placed anus, as in all Hirudineae except Acanthob- 

 della. 



For description of digestive tract, see Gratiolet, Ann. Sci. Nat, 



Ser. iv., vol. xvii., pp. 182, 188, 197; Brandt, Medizin. 



Zoolog., Bd. ii., p. 246. 

 For figures of the digestive tract of the Horse-leech, see Moquin 



Tandon, Monographic des Hirudinees ; Atlas, pi. v. fig. 1 1 ; 



Gervais and Van Beneden, Zoologie Medicale, 1859, P- ^^^• 



41. Medicinal Leech (Hirudo Medicinalis), 



Dissected so as to show its nervous system. 



A PART of the pharynx and the jaws are still left hi situ, and 

 a black bristle has been passed through the remaining part of the 

 pharynx, where it is embraced by the nerve collar. There are in 

 the Leech twenty-two ventral ganglia, the most anteriorly jilaced 

 one of which is connected by commissures with the supra-oeso- 

 phageal mass. This mass is seen above the pharynx, part of the 

 glandular and muscular walls of which have been removed to show 

 it, in sitM, and immediately posteriorly to the middle one of the 

 three jaws. In the narrow interspace between these two structures 

 is seen a minute mesial stomato-gastric ganglion, which is con- 

 nected with the supra-oesophageal ganglia, and sends nerves to 

 the semilunar saw-like jaw and its muscles ; and a similar gang- 

 lion similarly connected with the supra-oesophageal mass, may be 

 seen on either side, sending nerves similarly to either of the two 

 lateral jaws. Each lobe of the supra-oesophugeal mass gives off 

 three other nerves, whence the five eyes of either side and certain 

 other, probably sensory, organs, the 'becher-formige Organe' of 

 Leydig, are supplied. The first sub-oesophageal ganglion is much 



K 2 



