286 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



the inner and one from tlie outer surface of the kidney, and one from 

 below the pericardium . 



The heart is shown in Fig. 10 on Plate VI. The auricle has an 

 extremely thin wall formed of a pavement epithelium of flattened 

 cells with discoidal nuclei, within which is an open network of 

 muscle-fibres. The walls of the ventricle have a very similar 

 structure, except that the muscle-fibres are far more numerous and 

 the outer ones form a practically continuous layer next to the . 

 limiting epithelium. The auriculo-ventricular valve is formed by 

 a pair of small muscular membranes, which project into the cavity 

 of the ventricle where the auricle opens into it and leave only a 

 narrow slit between them. 



The aorta divides into anterior and posterior branches soon after 

 leaving the hinder end of the ventricle. The anterior aorta is large ; 

 it lies close to the inner side of the spermoviduct for the greater part 

 of its length, but bends away from it in front, passing to the ventral 

 nerve ganglia, where it divides in the usual manner into the 

 odontophoral artery, the pedal artery, etc. The pedal artery can be 

 traced backwards in the foot even beyond the posterior extremity 

 of the pedal gland ; it is situated immediately above the duct of 

 the pedal gland for most of its length. 



The Excretory System.— The pericardium communicates with the 

 exterior by means of the reno-pericardial duct, the kidney, the ureter, 

 and the mantle-cavity. The reno-pericardial duct projects into the 

 kidney from the inner and upper side of the pericardium about 

 opposite to the middle of the ventricle. (Its position is shown in 

 Fig. 10 on Plate VI.) It consists of a narrow duct, "33 mm, in length, 

 lined by a strongly ciliated epithelium. 



The kidney attains a length of about 5 mm., being rather more than 

 twice as long as the pericardium. Its hinder end extends upwards to 

 the rectum, as shown in Fig. 10. Internally its walls form a spongy 

 network of thin folds covered with excretory cells. 



The ureter arises from the extreme front end of the kidney. It 

 then runs backwards along the upper edge of the kidney to the 

 posterior extremity of the mantle-cavity, where it curves round and 

 passes forwards beside the rectum for about '5 mm. and then 

 opens. The secondary ureter is thus exceedingly short, as will be 

 seen from the figure. In front of the opening, however, the groove 

 which passes forwards to the mantle-edge beneath the rectum is 

 lined with a cubical epithelium, similar to that of the ureter itself. 



The Central Nervous System is shown in Fig. 4 on Plate VI. The 

 buccal mass is capable of being withdrawn through the nerve-ring, 

 the cerebral ganglia and commissure being situated immediately 

 above the jaw in the specimens examined. The cerebral ganglia 

 are united by a commissure measuring about "25 mm. in length. 

 The projecting anterior portion of each ganglion bears a small lateral 

 lobe on its outer side. The buccal ganglia are situated behind the 



