136 HUGH WATSON. 



lamella seems to be composed of a doable layer of peculiar 

 rounded or polygonal cells with thick walls. 



The hind end of the pedal gland is also enlarged to form a 

 vesicle in Rhytida/ Paryphanta,^ and Schizoglossa/^ 

 and indeed this is probably the case in all the genera of the 

 RhytididaB, for I have found such a vesicle in Natal in a as 

 well. Moreover, Rentier^ has shown that in Paryphanta 

 it contains a lai'ge fold similar to that in Apera, but appa- 

 rently less highly specialised in structure. In Testacella 

 there is also a dorsal fold ■' projecting into the duct at the 

 hind end of the pedal gland, but the structure of the fold 

 appears to be very different from that of Apera, and there 

 is no terminal enlargement of the gland to form a vesicle. 



Various possibilities suggest themselves with regard to the 

 function of the terminal vesicle of the pedal gland, and the 

 fold which it contains ; but so little is known about the physio- 

 logy of the gland in the carnivorous genera that such specu- 

 lations can have little value. It is better, therefore, simply 

 to state that the function of these structures is at present 

 unknown. 



THE NERVOUS SYSTEM. 



The centi-al nervous system of Apera consists of three 

 compact ganglionic masses joined by connectives. The first 

 of these is formed of the cerebral ganglia, the second of the 

 buccal ganglia, and the third of the pedal, pleural, and 

 visceral ganglia. 



The Cerebral Ganglia and Commissures. — As in nearly all 

 carnivorous snails and slugs, excepting Daudebardia'' and 



' Colliiige, W. E., ' Ann. Mag. Nat. Hist.' (7th ser.), 1901, vol. vii, 

 pp. 67, 68, pi. i, figs. 12, 13. 



2 CoUinge, op. cit., p. 70, pi. ii, figs. 21, 24; Min-docli, ' Trans. N.Z. 

 Inst.,' 1904, vol. xxxvi, p. 158, pi. vi, fig. 7. 



3 Muvdoch, R., ' Proc. Mai. Soc,,' 1901, vol. iv, p. 170. pi. xvii, fig. 10. 

 ^ • Zool. Jalirb.,' 1901, vol. xiv, p. 376, pi. xxvi, fig. 7. 



•^ Plate, L. H., ' Zool. Jahi-b.,' 1891, vol. iv, p. 525, pi. xxxii, figs. 17, 18. 

 8 Plate, op. cit., pp. 589, 593. 



