126 SUPPLEMENT ^ 



with the stomach is made by an extremely narrow orifice ; it 

 has a similar opening into the rectum, which latter proceeds 

 directly to the anus, which is very small, and pierced in the 

 last ring of the body. 



No author has spoken of a liver in the leech ; yet M. de 

 Blainville regards as such the cellular system, already men- 

 tioned, of a deep brown, which clothes externally, in the form 

 of a membrane, the greatest part of the intestine and stomach. 



The respiratory apparatus, according to the generality of 

 observers, does not exist in a specific manner in the leeches. 



The circulatory system is considerable and very complicated 

 in these animals : it is composed as usual of a venous and arte- 

 rial system, but there is no heart, properly so called. 



The venous system is formed of two very long vessels, with 

 their distinct parietes, situated imderneath each side of the 

 body, between the intestinal canal and the longitudinal stra- 

 tum of muscles of the external envelope. These vessels, 

 which are evidently larger in the middle than at the extremi- 

 ties, receive in their passage a great number of transverse 

 branches, some of which return from the tissue itself of the 

 animal, and others come from the vessel on the opposite side, 

 from which it follows that these two large veins and their 

 ramifications form a net-work with broad meshes on the back 

 of the leech. 



Towards the anterior extremity these two veins are con- 

 tinued in branches which curve upwards, and unite in the 

 middle and dorsal line to a smaller vessel, but with parietes a 

 little thicker, placed in a longitudinal fuiTOw, hollowed in all 

 the length of the intestine. This is the aorta, from which 

 spring, at a right angle from the two sides, the vessels des- 

 tined by their ramifications to carry the blood into all the 

 parts of the body of the animal, but especially to the parietes 

 of the intestinal canal. 



The reproductive apparatus, or system of generation, is 



