60 THE LEECH. 



somite. It is wide at its base, narrow and tubular 

 in its distal part, and can be protruded some dis- 

 tance through, the male genital aperture in the 

 second annulus of this somite. 



The female organs lie entirely in the seventh somite. 



a. The ovaries are a pair of minute filamentous bodies, 



enclosed in small spherical sacs, lying close to 

 the mid- ventral line. 



b. The oviducts are a pair of slender tubes leading 



from the sacs of the ovaries, which unite to form 

 a much-convoluted duct surrounded by uni- 

 cellular-gland cells, and opening into the vagina. 

 The right oviduct passes under the nerve-chain. 



c. The vagina is a thick-walled tube, opening to the 



exterior at the female genital pore in the second 

 annulus of the seventh somite. 



E. The Nervous System. 



The nervous system consists of a pair of supra- oesophageal 

 ganglia, a nerve-collar, and a double gangliated cord ex- 

 tending the whole length of the ventral body- wall. From the 

 ganglia nerves run outwards to the various parts of the body. 



1. The supra-cesophageal ganglia are a pair of closely 



apposed bodies in the dorsal wall of the anterior 

 end of the pharynx, immediately behind the jaws. 

 They supply the jaws, the eyes, and other parts of 

 the anterior end of the body. 



2. The nerve-collar is very small, and closely surrounds 



the anterior end of the pharynx. 



3. The ventral nerve-chain lies in the ventral- sinus, which 



must be slit open to expose it. It consists of two 

 halves very closely apposed in the median plane. 

 There are twenty-three pairs of ganglia, lying in 

 the first annuli of their respective somites. The 

 successive pairs of ganglia are much closer together 

 at the two ends of the body than they are along the 

 middle portion of its length. 



