128 SUPPLEMENT 



siderable and very long, is directed backwards for its first 

 half, then forward for the second. These two parts are 

 cemented one against the other, and towards the place 

 where the ovaries are, the extremity gives issue to the excita- 

 tory organ. The latter veiy long, slender, and cylindrical in 

 a part of its extent, claviform at its extremity, issues forth by 

 the anterior genital orifice, probably from the contraction of 

 the sheath, which appears to be of a muscular tissue. 



We have to state that this description, differing consider- 

 ably fi'om what we find in the works of many authors, is 

 taken from M. de Blainville, who had the fortunate opportu- 

 nity of dissecting a leech taken in the act of coupling, and in 

 which consequently all the parts were in the greatest state of 

 development, so that at all events we may rely upon its gene- 

 ral truth. This part, however, of the anatomy of this animal 

 involves much difficulty. The nervous system of the leech 

 is pretty nearly similar to that of the lumbrici, and the rest of 

 the class. Placed on the middle abdominal line in the cellu- 

 lar tissue, which separates the intestine from the sub-cutane- 

 ous muscular stratum, it is composed of a certain number of 

 ganglia placed in file, and furnishing, beside the cords of 

 communication in front and behind with each other, some 

 transverse threads for the external envelope. The number of 

 these ganglia appears to be very variable. The first, much 

 larger than, and differently composed from, the others, is 

 immediately on the under lip. Besides the threads which it 

 furnishes to the surrounding parts, there issues forth on each 

 side a thick cord, which is continued with a cephalic or epi- 

 labial ganglia scarcely thicker than itself, and which gives 

 out the nerves of the upper lip. 



Each of the following ganglia is of a lozenge form ; the an- " 

 tenor and posterior angles furnish the double cords which 

 continue the nervous system along the belly, and from the 



