THE CARNIVOROUS SLUGS OF SOUTH AFRICA. 175 



" tail muscle/' in connection with the foot, will remain as the 

 direct continuation of the buccal retractor, but it will still be 

 situated towards the right side of the animal. In Schizo- 

 glossa we have a slug in which the degeneration of the shell 

 has only partially taken place, and the chief muscle-fibres 

 are still attached to the reduced colmnella ; and it would be 

 difficult to draw a diagram illustrating the theory which I 

 have just set forth more aptly than does Murdoch's figure of 

 the retractor muscles of Schizoglossa novoseelandica 



Several pairs of buccal protractors stretch from the outer 

 layer of the walls of the buccal mass to the skin of the 

 anterior part of the head. The longest and most important 

 of these are inserted on each side just in front of the odonto- 

 phore and below the opening of the oesophagus (PI. XXI, 

 figs. 129-134). These protractor muscles, together with the 

 intrinsic muscles of the buccal mass, serve to protrude the 

 odontophore, which seems to be protrusible in all the species 

 of Apera. But even in A. gibbonsi the protractors are not 

 very thick ; and this is not surprising, for it is evident that 

 less powerful muscles will be required to protrude the odonto- 

 phore than to retract it after the teeth have become fixed in 

 the skin of a worm. 



The Oesophagus and Ckop. — In Apera gibbonsi and A. 

 parva the oesophagus is very short and broad, and merges 

 imperceptibly into the crop (PI. XXI, figs. 129-131). The 

 latter is fusiform in these species, and after increasing in 

 width it gradually tapers again towards the openings of the 

 hepatic ducts, its broadest part being about twice as far from 

 these ducts as from the opening of the oesophagus into the 

 buccal mass. 



In the remaining species the oesophagus is long and 

 narrow, as will be seen from figs. 132 to 134. At its posterior 

 end it enlarges rather abruptly to form the crop, which is 

 usually widest near the front end, but remains fairly broad 

 almost as far back as the ducts of the liver, and then narrows 

 ' 'Proc. Mai. Soc," 19U0, vol. iv, pi. xvii, fig. 10. 



