316 Proceedings of the .Royal Society of Edinburgh. [Sess. 
in the same relative position as the normal one — that is, ventral and slightly 
posterior to the ocular tentacle (Tent.P.L.). The blind end of the vas 
deferens is situated immediately below the papilliform area of the skin 
indicated by the -fi in fig. 1 — that is, about 2 5 mm. posterior and slightly 
dorsal to the external aperture of the penis. There is also on the left side 
a groove (Ep.Gr.) * in the skin, the course of which corresponds to that of 
the groove of the right side, already described (p. 314). The blind end of the 
vas deferens lies very close to the dorsal margin of this groove, just before 
the latter bends ventrally on approaching the genital orifice. 
Examination of the internal structure of these extra organs shows that 
they are quite normally and perfectly developed. The flagellum shows, in 
section, the usual longitudinal curved or scroll-like internal fold, exactly as 
in the normal organ, where its function is presumably to aid in moulding the 
spermatophore. The wall of the flagellum consists of an internal granular 
epithelium surrounded by a thick layer of longitudinal and circular muscle 
fibres. The vas deferens is lined by a folded epithelium, outside which 
is a thin sheath of muscular and connective tissue. 
The penis has the usual structure (see p. 313) ; it possesses a thin outer 
sheath (fig. 3, P.Sh.O.), which surrounds the much stouter inner sheath 
(P.Sh.I.), the latter having about the middle of its length a muscular tubular 
introvert (Intr.). Enclosed by the proximal part of this inner sheath, the 
inner surface of which presents the usual rugose appearance, is a muscular 
copulatory organ (C.O.), on which the vas deferens opens. This organ is 
fully as large (3 mm. long) as that of the right side of the same specimen 
and of other specimens examined. In the distal part of the inner sheath 
there are also longitudinal folds exactly as in the normal organ (see fig. 4). 
One of these folds ends in a somewhat tongue-like depressed papilla (Pa.), 
about a millimetre wide, the distal margin of which is raised well above the 
general surface of the sheath. In all the normal specimens which I have 
examined, a papilla similar in form and size is also present, and lies close to 
the point at which the penis enters the atrium. Its position and structure 
suggest that it forms a rudimentary valvular arrangement serving to 
partially or completely close the penial aperture, especially when the lips of 
the latter are in the contracted condition. But whatever its function may 
be, this papilla apparently marks the distal end of the penis ; beyond lies 
the atrium. In the supernumerary penis this papilla f is about 2 5 mm. 
* This groove is present in normal specimens on both right and left sides. 
t It is interesting to note that the papilla is situated upon the internal wall, i.e. the 
wall adjacent to the middle line, in both the normal and supernumerary penes, another 
instance of their symmetrical relations. 
