120 THE SNAIL 



sacculated female or oviducal and a much narrower male or spermaducal 

 channel. Passing <along the top of the common duct is the finer spermathecal 

 duct, which gives off a long coiled diverticulum and is continued on to the base 

 of the albumen gland, where it ends in a swollen sac, the sperrnatheca or 

 receptaculum seminis. Note the sinuous hermaphrodite duct from the herma- 

 phrodite gland or ovotestis, a yellowish body which lies embedded in the second 

 coil of the liver. The hermaphrodite duct leads into the base of the tongue- 

 shaped albumen gland, where the common duct arises. Trace the common 

 duct forward and note that its male and female portions separate off as a vas 

 deferens and an oviduct. The oviduct is short and thick ; it leads into the 

 muscular vagina, into which the spermathecal duct, the dart sac, and a pair of 

 tufted mucous glands open. The vagina opens to the exterior, along with the 

 penis, by the common genital aperture. Trace the vas deferens forward from 

 its point of origin and note that it passes into a muscular penis provided with a 

 long flagellum and a retractor muscle. The penis is protrusible and opens at 

 the common genital aperture. 



Make a drawing showing the alimentary and reproductive systems. 



C The Nervous System. 



Cut through the oesophagus, just behind the buccal mass, and remove the 

 alimentary tract. Pull the buccal mass forward and pin it down. 



The supra-oesophageal or cerebral ganglia are incompletely fused and lie 

 over the oesophagus. From each ganglion the following nerves pass off : — 



(a) The buccal nerve, which enlarges to form a buccal ganglion situated on 

 the posterior surface of the pharynx on each side of the oesophagus. 

 The buccal ganglia are connected by a transverse commissure passing 

 under the oesophagus. 



{b) The internal labial nerve. 



(c) The external labial nerve. 



(d) The facial nerve. 



(e) A nerve running next to the facial and supplying the anterior body-wall. 

 (/) The optic nerve to the eye tentacle. 



(g) A nerve passing to the otocyst which lies embedded in the pedal ganglion. 



The right cerebral ganglion also gives off a nerve, the penial, supplying the 

 penis. 



Passing round the oesophagus and connecting the cerebral ganglia to the sub- 

 cesophageal mass is a pair of commissures. The sub- oesophageal mass consists 

 of the fused pleural, pedal, and visceral ganglia. The cerebro-pleural commis- 

 sure connects the cerebral to the pleural ganglia, and the cerebro-pedal commis- 

 sure connects the cerebral and pedal ganglia. The pedal ganglia give rise to 

 pedal nerves supplying the foot. The visceral ganglia give rise to a left pallial 

 nerve, a median pallial nerve, and a right pallial nerve (passing over the 

 common duct) to supply the mantle, and a genital nerve supplying the common 

 duct. 



Make a drawing of the nervous system. 



