240 HUGH WATSON. 



in Dau debar dia it is extremely short. In Testae el la the 

 vagina is not surrounded by any glandular tissue ; in Dau de- 

 bar dia the anterior end of the vagina is encircled with 

 glandular tissue, as in Hyalinia. In Testacella the penis 

 passes between the right tentacular retractors; in Daude- 

 bardia, as in Hyalinia, it lies outside both retractors. In 

 Testacella the genital opening is on the side of the head; 

 in Dau debar dia and Hyalinia the opening is further 

 back. In short, the two genera only resemble each other 

 in a few features which would be likely to be developed in 

 any vermivorous form, and they differ in nearly every other 

 respect. 



The dissimilarity in the nervous system is alone almost 

 sufficient to prove that the carnivorous characters of Testa- 

 cella have been acquired independently of those of Daude- 

 bardia. It is a general rule in the animal kingdom that 

 nerve-ganglia tend to unite and not to separate; therefore we 

 cannot derive Testacella, with its distinctly separate 

 abdominal and right parietal ganglia, from forms in which 

 these ganglia are more or less united ; and this is the case in 

 Hyalinia as well as in Daudebardia, notwithstanding 

 Plate's statement to the contrary. 



Now, if Testacella is not allied to Daudebardia, there 

 is no reason for supposing it to have been derived from the 

 Zonitidse. This has only been thought to be the case 

 because Daudebardia has almost certainly been evolved from 

 that family, and Testacella was supposed to be related to 

 Daudebardia. In Testacella, as in Apera, the carni- 

 vorous characters have reached a very high state of specialisa- 

 tion, and it is therefore more probable that Testacella has 

 been evolved from some family of carnivorous snails. 



Beutler^ considers that Paryphanta may be ancestral 

 to Testacella. Now Paryphanta certainly resembles 

 Testacella much more closely than does Daudebardia. 

 Indeed in its visceral ganglia it is more like Testacella 

 than Apera. But Testacella dijffers from Paryphanta, 

 ' ' Zool. Jiilirl)..' 1901, vol. xiv, p. 407. 



