282 DESCRIPTION OF THE PLATES. 



b. Shield and organs in connection with it. 



c. Stomach and bilobed liver, arranged upon the animal's left. 



d. Generative apparatus arranged upon the animal's right. 



e. Nerve-collar, consisting of two cerebral ganglia placed above, or rather 



at the sides of, the oesophagus, and two pairs of ganglia placed 

 below it, and united with the upper pair by connectives. The two 

 cerebral ganglia are connected by a flat commissure, and with the 

 infra-oesophageal ganglia by a double connective, the posterior cord 

 of which joins the posterior part of the mass or visceral ganglia, 

 whilst the anterior cord joins the anterior or pedal ganglia from which 

 nerves pass off to the foot. 



f. Stomatogastric ganglion of right side placed below the oesophagus, 



where it enters the buccal mass together with the duct of the salivary 

 gland. The ganglion is connected by a long and delicate com- 

 missural cord with the supra-oesophageal ganglion of its own side, 

 and it gives off nerves to the buccal mass, to the oesophagus, and 

 to the duct of the salivary gland. 



g. Salivary gland. 



h, Buccal mass containing the ' tongue ' or ' odontophore.' 



i. Semper's organ. It is of very large size in this Slug, small in Helix, 

 Arion, Lymnaeus, and has only been detected in Ptdmonata. It 

 consists of four to five lobes composed of cells, resembling those 

 in the salivary or supra-pedal glands, held together by a network 

 of connective tissue and a membrane. According to Sochaczewer 

 (Z. W. Z. xxxv. 1 88 1, p. 35), it receives two nerve twigs from the 

 labial nerves, and is not, as Semper supposed, richly supplied with 

 nerves. A ganglion has been detected by Sarasin (Arb. zool. zoot. 

 Inst. Wurzburg, vi. 1883, p. 95) lying in the oral lobes and sending 

 processes into this gland. It occurs also in Pulmonata Basommato- 

 phora, in which Semper's organ is absent. 



j. Coecal projection at pyloric end of stomach. 



k. Liver consisting of two lobes opening each by a single duct close to 

 the pylorus. 



/. Intestine passing from the pylorus to end a little in front of and above 

 the respiratory inlet. Its two first convolutions have been separated 

 from the liver and reproductive apparatus. As it approaches the 

 dorsal integument and shield it describes a curve like an Italic S. 

 In the first loop of this 5 is seen the origin of the retractor muscles 

 of the buccal mass and labial tentacles ; at its opposite extremity 

 arises a straight coecum, y. 



M. Respiratory orifice, with the ' rectum ' curving round to open a little 

 above and anteriorly to it. To the right of the rectum is seen the 

 duct of the renal organ. 



