SANGUISUGA. 



ring to the structure of analogous parts found in other Anneli- 

 dans. In Aphrodita aculeala, for example, the representatives 

 of the wide pouches met with in the leech are narrow and 

 branched tubes, terminating in blind extremities, to which it 

 is usual to assign the office of separating a biliary secretion ; 

 and according to this view the caeca of the leech may be re- 

 garded as the simplest rudiments of the assistant chylopoetic 

 glands; the first pair, from their proximity to the mouth, 

 may be destined to furnish a salivary fluid, and the succeeding 

 ones may be intended to perform the functions of biliary 

 follicles. 



The small size of the intestine, when compared with the 

 capacious stomach described above, is remarkable; it com- 

 mences by a minute orifice from the termination of the diges- 

 tive cavity, and, becoming slightly enlarged, passes in a straight 

 line, lodged between two posterior caeca, to the anus, which is 

 an almost imperceptible aperture placed at the .root of the 

 posterior sucker ; four small and apparently glandular masses 

 are appended to this short canal, but their nature is unknown. 

 The entire alimentary apparatus is retained in situ by numer- 

 ous membranous septa, passing between its outer walls and 

 the muscular parietes of the body. 



The operation of digestion is extremely slow, notwithstand- 

 ing the rapid and excessive manner in which the leech fills its 

 stomach ; a single meal of blood will suffice for several months, 

 nay, more than a year will sometimes elapse before the blood 

 has passed through the alimentary canal in the ordinary man- 

 ner, during all which period so much of the blood as remains 

 undigested in the stomach continues in a fluid state. This 

 accounts for the reluctance of the leech, after being used to 

 abstract blood, to repeat the operation ; it not only being 

 gorged at the time, but provided with a sufficient supply for 

 so much longer. Indeed, the true medicinal leech does not 

 seem to take any solid aliment, but subsists on the fluids of 

 frogs, fish, &c. 



The organs provided for respiration are a series of mem- 

 branous pouches, communicating externally by narrow ducts 

 or spiracles, as they might be termed, into which aerated water 

 is freely admitted. These respiratory sacculi, in the leech, 

 are about thirty-four in number, seventeen being visible on 

 each side of the body ; they are extremely vascular, and in 

 connection with every one of them there is a long glandular- 



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