31. 



between the stomacla and intestine nearly to tlie pedal ganglia, 

 and surroiind tlie digestive glands as well as dip in between their 

 lobes. The opening of the genital duct, figure 23, gd, has al- 

 ready been described in connection with the excretory organ. 



The sexes are separate aiid, when the genital products 

 are abundant, they may easily be distinguished by the color of 

 the genital mass surrounding the digestive glands. This portion 

 is chocolate brown in fe^nales and yellow in males. 



NERVOUS SYSTEM. 

 Figures 4 and 5. 

 The cerebral ganglia fig. 4, eg. united in front of the 

 oesophagus by a very broad commissure, which differs very little 

 in structure from the ganglia themselves, lie just posterior to 

 the ventral side of the anterior adductor raascle. Each ganglion 

 is almost circular in transverse section and gradually tapers 

 posteriorly into the cerebro-visceral commissure. So gradually 

 does this tapering take place, that it is impossible to deterroine 

 where the ganglion ends and the commissure begins. Even in struct- 

 ure there is onl3'- a difference in degree, there being proportional- 

 ly more nuclei in the ganglion than in the commissure. Posterior 

 ly each commissure gives place, in the same gradual way, to a visce3 

 al ganglion. The visceral ganglia, vg, lie anterior to the 



