184 HUGH WATSON. 



The Duct. — The duct of the pedal gland is semi-trans- 

 lucent, and can be seen running- along the centre of its upper 

 surface. Near the opening of the gland the duct usually 

 lies more deeply (PI. XIV, fig. 63), but elsewhere the 

 glandular tissue is restricted to its sides and lower surface, as 

 shown in PI. XIII, fig. 59. Where the glandular tissue is 

 less abundant the exposed surface of the duct often shows a 

 tendency to have alternate swellings and constrictions. In 

 Apera gibbonsi this culminates in a close convolution of the 

 posterior part of the duct (PI. XIII, fig. 58), which reminds 

 one of the somewhat similar convolution of part of the duct 

 in Testacella.^ On the upper sui-face of the anterior half of 

 the gland in A. dimidia, two brownish lines can often be 

 seen running along, one on each side of the duct, at its junc- 

 tion with the glandular tissue. 



In section the duct is approximately circular, without any 

 folds on its floor (PL XIII, figs. 59, 60, PI. XIV, fig. 63). In 

 this respect it resembles that of Testacella, and differs from 

 that of Daudebardia, for in the latter genus, as in most 

 herbivorous snails and slugs, the floor of the duct has two 

 longitudinal folds enclosing a median groove, and the gland- 

 cells only open into this groove, instead of all round the duct.- 

 In Paryphanta hochstetteri [Pfr.) traces of the folds 

 and median groove seem to occur, but only towards the 

 anterior end of the duct."' The duct is lined by an epithelium 

 composed of small cubical cells, and this is surrounded by two 

 thin muscular layers, the fibres of the inner layer running 

 round the duct, while those of the outer layer are longitu- 

 dinal. Both layers of muscles occur inside the glandular 

 tissue. 



The Terminal Vesicle. — After becoming gradually narrower 

 the gland widens again at the hind end to form an oval or pod- 

 shaped vesicle (PI. XIII, figs. 52-57). In length this vesicle 



' See de Lacaze-Duthiers, ' Arch. Zool. Exper.' (2nd ser.), 1887, vol. v, 

 pi. xl, fig. 95. 



' Plate, L. H., ' Zool. Jabrb.,' 1891, vol. iv, p. 525, pi. xxxii, fig. 16. 

 ■» Beutler, B., • Zool. Jalirb.." 1901. vol. xiv, p. 376. pi. xxvi, fig. 9. 



