THE CABNIVOEOUS SLUGS OF SOUTH AFRICA. 191 



this hypothesis must remain very doubtful until a sufficient 

 number of specimens of this rare species has been collected in 

 order to justify the dissection of the penis. In a full-grown 

 example of A. gibbonsi rubella from Durban, the penis 

 was found to be quite vestigial. 



As so few full-grown specimens of Apera have been 

 collected, I have only felt justified in examining the internal 

 structure of the male organs in two forms, namely, A. 

 dimidia and A. gibbonsi rubella. No penis-papilla is 

 present in either of these species, but in both forms the inner 

 surface of the muscular wall of the penis is completely covered 

 by numerous small papillae, as shown in PI. XXIII, fig. 145. 

 These papilla? are diamond-shaped in transverse section, and 

 each ends in a short point. The structure of the papillae is 

 very similar in the two species, and is shown in PI. XXII, 

 fig. 142, which represents a photomicrograph of the inner half 

 of a single papilla from the penis of A . gibbonsi rubella. 

 In this form the papillse become considerably smaller around 

 the opening of the epiphallus, and within the opening they 

 become much narrower in proportion to their length, 

 changing, in fact, from papillee into filaments. These fila- 

 ments occur throughout the entire length of the epiphallus. 

 They do not, however, arise from all parts of the inner 

 surface of the wall of the epipHallus, but are arranged in 

 longitudinal rows, of which there are about fourteen in the 

 specimen that I examined. Between the rows the wall of the 

 epiphallus is extremely thin. In Apera dimidia the epi- 

 phallus has a different structure, being lined by numerous 

 minute papilla?, closely arranged, and not unlike the papillae 

 lining the penis, only much smaller. It is somewhat remark- 

 able that while the inside of the penis is so very similar in 

 the two species, the inside of the epiphallus should present 

 such a marked contrast. 



The retractor of the penis is attached to its posterior end, 

 and arises from the roof of the body-cavity near the mid-dorsal 

 line. In Apera burnupi, A. sexangula, A. purcelli, 

 and A. parva, it is very long and narrow, arising in A. 



