THE CARNIVOROUS Sr,UGS OF SOUTH AFRICA. 227 



covered when the greater portion of the body is under the 

 surface ot" the ground, or inside its victim's shell. 'J'he anus 

 will move back with the respiratory opening, and. the rectum 

 will thus be directed posteriorly (text-fig. 5^ cf. c and d, p. 183) . 

 With the degeneration of the shell the pallial organs will 

 become modified, and the posterior position of the pulmonary 

 veins may pull round the auricle until it lies posterior to the 

 ventricle, as in Testae ell a and a few other genera (text- fig. 

 6, p. 244). The organs which formerly occupied the viscex*al 

 hump will become reduced in size and pushed forward into 

 the general body-cavity. The pressure of these will retard 

 the backward growth of other organs such as the receptaculum 

 seminis, and it is therefore not surprising to find that the 

 slugs have as a rule shorter receptacular ducts than the snails 

 to which they are probably most nearly allied. The columellar 

 muscle will disappear with the degeneration of the shell, and 

 the various retractors that originally arose from it will become 

 attached to different parts of the skin, which will become 

 thickened to take the place of the shell (see p. 126). And 

 as the anterior part of the body becomes lengthened, the 

 origins of the tentacular and penial retractors will tend 

 to move forwards. Thus the mere fact that animal food 

 is less easily accessible than vegetable food may lead to 

 profound changes in the anatomy of a snail Avhich becomes 

 carnivorous. 



When the snail has approached its victim it will require to 

 feel exactly where to attack it with its i-adula, and will, if 

 possible, try to prevent the animal escaping until the teeth 

 are fixed in its flesh. Accordingly we find that nearly all the 

 carnivorous genera have a pair of special feelers at each side 

 of the mouth beneath the lower tentacles. In Euglandina 

 these feelers are very long and are supposed to be used for 

 prehension, but according to F. M. Woodward ^ their function 

 in Natalina caffra [Fer.) is probably purely tactile. Miss 

 Davies"'' has recently discovered that in Paryphanta com- 



1 ' Proc. Mai. Soc.,' 1895, vol. i, p. 271. 



- ' Proc. Roy. Soc. Victoria,' 1913, vol. xxv, p. 225. 



