THE OAENIVORUUS SLUGS OF SOUTH AFRICA. 151 



than ill most genera, probably because they innervate a 

 region of the body which is greatly reduced in Apera. The 

 origin of these nerves is shown in PI. XV, figs. 73 and 74, 

 and their distribution iu A. dim idia will be seen fi'om fig. 75. 



One important nerve arises from the right parietal or supra- 

 intestinal ganglion, not far from its junction with the other 

 visceral ganglion, and innervates the right wall of the mantle- 

 cavity. This may be regarded as the right pallial nerve. 

 The corresponding left pallial nerve is more slender, and 

 arises from the outer or parietal portion of the left visceral 

 ganglion. This nerve innervates the left wall of the mantle- 

 cavity. From the median or abdominal portion of the left 

 visceral ganglion two large nerves arise close together. That 

 to the left becomes closely united for some distance with the 

 buccal retractor in Apera dimidia, and then runs back on 

 the right side of the rectum, and eventually branches around 

 the anus and respiratory orifice. The right abdominal nerve is 

 joined to the aorta for almost the whole of its length, but at its 

 hind end the nerve leaves the blood-vessel and enters the 

 diaphragm, which it probably innervates. Beyond this the 

 nerve becomes attached to the adjacent wall of the peri- 

 cardium, and can be traced backwards to a point just behind 

 the opening of the reno-pericardial duct. The other nerves from 

 the visceral ganglia are also attached to the aorta for some 

 distance, the left pallial nerve being the first to become free. 

 One or two small additional nerves can be seen with a stronsr 

 objective to leave the visceral ganglia and run along in the 

 tissue surrounding the aorta, but these are so extremely fine 

 that I was unable to trace them far. Thus only four nerves 

 of any importance arise from the visceral ganglia in Apera — 

 two pallial and two abdominal ; and inasmuch as the abdominal 

 portion of the left ganglion is probably itself formed from 

 the union of the sub-intestinal ganglion with the original 

 median abdominal ganglion,^ it follows that there is but one 

 nerve corresponding to each original ganglion on the visceral 

 loop. 



' Pelseneer. P.. 'Mem. Acad. Roy. Belg.,' 1901, ex vol. liv. pp. 47. 48. 



