NATURAL HISTORY OF THE MUSSEL 45 



stimuli (paired ganglia), all connected to one 

 another, and giving off branches to the various 

 organs in proximity. One centre of stimulus is 

 situated in what may be called the head region, 

 another in the foot, while the third supplies the 

 digestive and reproductive organs, the gills, and 

 part of the mantle ; fusing in this last organ, with 

 branches from the head ganglia. 



Lastly, we have the reproductive organ, the 

 greater part of which is situated in the substance 

 of the mantle. The remainder, which is most 

 readily seen when the mussels are in a spawning 

 condition, is situated on the sides of the centre or 

 body proper, i.e. where the lobes of the mantle 

 pass off from the central body. A number of 

 ducts in each mantle-lobe collect the genital pro- 

 ducts into a common tube at a point close to the 

 anterior end of the cavity of the heart, below the 

 retractor muscles of the foot. From this point 

 the ducts pass inwards, till they open at the genital 

 papillae towards the hinder end of the central 

 body, at the inner angle of the attachment of the 

 gills, represented in section by the central apex of 

 the letter W. 



The sexes of the mussel are distinct, although 

 the arrangement of the male and female organs is 



