THE CARNIVOROUS SLUGS OF SOUTH AFKICA. 231 



in these forms, and possibly in others also, digestion takes 

 place partially within the lobes of the liver. In neai'ly all 

 the carnivorous genera the length of the intestine and rectum 

 is more or less reduced. 



Finally, Simroth considers certain peculiar connections 

 between the genital ducts of a few of the carnivorous genera 

 to be modifications to facilitate self-fertilisation, and he attri- 

 butes this to the somewhat isolated life which a vermivorous 

 slug is likely to lead. But I have not found these modifica- 

 tions in the forms which 1 have examined, and it remains to 

 be proved whether they are at all general among the 

 A g n a t h a . 



Such are the changes which are likely to take place in the 

 organisation of a snail when it acquires carnivorous habits. 

 We are now in a position to discuss whether Apera, Testa- 

 cell a, and other predaceous forms, are really closely related 

 to one another, or whether their resemblance is merely due 

 to the fact that thev have all become carnivorous. 



The Phylogeny of Apera and other Naked Carnivorous 



Slugs. 



I think that Simroth is the only author who has suggested 

 that the genus Apera has been evolved directly from an 

 herbivorous slug. As already mentioned, he put forward the 

 theory that Apera might have been derived from the 

 Janellidas. But Plate^ has shown that the slugs belonging 

 to this family differ from most of the Stylommatoph ora, 

 not only in being without lower tentacles, but in other 

 important characters, such as the respiratory tissue, which 

 takes the form of numerous fine tubes radiating from the 

 mantle-cavity and recalling the trachea of arthropods. Now 

 Apera possesses none of these features. Moreover, it Avould 

 be difficult to imagine a radula more unlikely to develop 

 carnivorous characters than that of Jan el la, with its 



' ' Zool. Jahvb.,' 1898, vol. xi, pp. 193-280, pis. xii-xvii. 







