188 Description of the Plates. 



forward so as to lie between the generative apparatus on the right 

 and one of the salivary glands on the left hand. One of the lower 

 tentacles is seen on the right side in the interspace between the 

 right eye-bearing tentacle and the vestibulum of the reproductive 

 system. 



a. Locomotive disk or ' foot' passing upwards at the sides into 

 the general muscular envelope of the various organs of the 

 animal's body, from which it is limited off by a furrow. 

 Its internal circular coat is raised into two corrugated 

 ridges along the middle line for the greater part of the 

 length of the body by the underlying mucous gland. This 

 gland has its bilaterally symmetrical halves arranged on 

 either side of a single duct, which again is underlaid by a 

 large venous sinus, very visible in the living animal along 

 the middle line of the foot inferiorly. 

 h. Shield and organs in connection with it projecting out 

 beyond and above the general muscular envelope of the 

 body. 

 c. Stomach arranged, together with the two lobes of the liver, 



upon the animal's left. 

 (I. Generative apparatus arranged upon the animal's right. 



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



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

 placed below it, and connected with the upper pair by com- 

 missural cords. The two superiorly placed ganglia are con- 

 nected with each other by a flat commissural band; and 

 with the suboesophageal ganglia by a double commissure, 

 the posterior cord of which joins the upper or parieto- 

 splanchnic part of the mass formed by the fusion of the 

 two inferiorly placed pairs of ganglia into a single centrally 

 perforated body, whilst the anterior cord joins the more 

 inferiorly placed or pedal portion from which nerves are seen 

 to pass off" to the foot. The functions of the supra-oesopha- 

 geal ganglia may be judged of by the distribution of its 

 nerves to sensory organs. The nerves which the parieto- 

 splanchnic ganglia gave off to the retractor muscles, as well 

 as to the parts their name denotes, have been removed in 

 the dissection. 



f. Stomatogastric ganglion of right side placed in the angle 



