190 HUGH WATSON. 



bends round and runs up the side of the penis. In Apera 

 gibbon si the vas deferens is rather thick excepting near the 

 vestibule, where it has the more usual form of a very slender 

 duct. In this species, and also in A. dimidia, before the 

 vas deferens unites with the posterior end of the penis, it is 

 slightly swollen for a distance equal to about one-third of the 

 length of that organ, thus forming a rudimentary epiphallus. 

 In A. sexangula this swollen part is very much shorter, 

 and bears at its anterior end a minute flagellum, which, like 

 the vas deferens itself, is closely applied to the side of the 

 penis (PI. XXIII, fig. 149). 



The penis passes between the retractor muscles of the 

 right upper and lower tentacles (PL XIII, figs. 52-57). 

 In this respect Apera resembles Testacella, Trigono- 

 chlamys, Poiretia, Streptostyla, Strebelia, Rhytida, 

 and Paryphanta, and differs from Daudebardia, Plu- 

 tonia, Selenochlamj^s, Natalina, Delos, andthe Strep- 

 taxi dfe, in which the reproductive organs are on the right of 

 both retractors, as was first shown by Pfeffer, Simroth, and 

 Murdoch. In Apera dimidia the penis is fairly short, but 

 a little swollen posteriorly (PI. XXIII, fig. 147). In A. 

 parva it is about 4 mm. in length, and somewhat fusiform 

 (fig. 146). In typical specimens of A. gibbonsi from Zulu- 

 land, the penis is also short (fig. 143), but in the other races 

 of that species it is very long and twisted in a peculiar 

 manner (fig. 144). In A. sexangula the penis is long and 

 very narrow, excepting at the posterior end, where it is broad 

 and somewhat flattened (fig. 149). In A. burn up i the 

 anterior part of the penis is also narrow, but it is much 

 shorter than in A. sexangula, and more or less twisted. 

 The posterior broader portion, on the other hand, is longei*, 

 and appears to be double, OAving to the presence of a deep 

 longitudinal groove on one side ; and the vas deferens dis- 

 appears into this groove about 5 mm. in front of the end of 

 the penis (fig. 148). Possibly this peculiar arrangement may 

 be due to the broad sides of the penis having arched over the 

 end of the vas deferens and joined each other above it ; but 



