48 THE LEECH 



d. The vesioTilse seminales are a pair of convoluted 



tubular bodies with thick white walls, lying in 

 the sixth somite. They secrete a substance by 

 which the spermatozoa are aggregated into 

 spermatophores. Prom their inner sides short 

 ducts lead to the base of the penis, the duct of the 

 right side passing under the nerve-chain. 



e. The penis is a pyriform body lying in the sixth 



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

 in its distal part, and can be protruded for some 

 distance from the male genital aperture in the 

 second annulus of this somite. 



2. The female organs lie entirely in the seventh somite. 



a. The ovaries are a pair of minute filamentous bodies 



enclosed in small spherical sacs, and placed in 

 the seventh somite close to the mid-ventral line. 



b. The oviducts are a pair of slender tubes leading 



from the sacs of the ovaries, and uniting to form 

 a much convoluted duct, which opens into the 

 vagina. The right oviduct passes under the 

 nerve -chain. 



c. The vagina is a muscular tube opening to the 



exterior at the female genital pore, in the second 

 annulus of the seventh somite. 



B. The Nervous System. 



The nervous system consists of a pair of supra-oesophageal 

 ganglia, a nerve collar, and a double chain of ganglia extend- 

 ing the whole length of the ventral surface. From the ganglia 

 nerves run outwards to the various parts of the body. 



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



apposed bodies placed 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. 



