THE CARNIVOROUS SLUGS OF SOUTH AFRICA. 



145 



the left cerebro-buccal connective would become stretched, 

 and would consequently retard the rotation of the buccal 

 ganglia to some extent, so that they would come to lie slightly 

 to the left of the opening of the cesophagus and the median 

 line of the odontophore.^ The result of this would be that 

 the nerves from the buccal ganglia would slope obliquely to 



Text-fig. 1. 



-■ Cerebro-buccal connective. 



Opening of cesophagus. 



Buccal ganglia. 



Odontophoral nerves. 



Centre of odontopliore. 



Diagram illustrating the possible origin of the asymmetry of the 

 odontophoral nerves of Apera. 



the right, as shown in the accompanying diagram, and this 

 would tend to shift their orig-in to the rig-ht. When the shell 

 became degenerate and the animal assumed a symmetrical 

 form, the odontophore would tend to return to its original 

 condition and to lie in a straight line between the mouth and 

 the buccal retractor- ; but it might be a long time before the 

 buccal nerves moved back again to their symmetrical position. 

 Now, as I shall attempt to prove later, it is not improbable 

 that Apera may have been evolved from a group of 



' Cf . Plate, L. H.. ' Zool. Jahrb..' 1891. vol. iv, pi. xxxvii, fig. 102. 



- The effect of the slightly asymmetrical origin of the buccal re- 

 tractor would be counteracted by the pressure of the reproductive 

 organs on the right side. 



