147 
opening of the size usual in trematodes (fig. 1,5). The cavity of this 
body forms a part of the genital sinus and its function is to receive the 
common genital duct (fig. 2, 9), which approaches it from behind and a 
little to the right. On the opposite or anterior side of the genital sinus 
and somewhat to the left is a large branched pocket (fig. 2, 4) of vary- 
ing form with thin, non-muscular walls, the actual size and form of 
which is very different in different individuals. 
The exact method by which this complicated apparatus operates 
during copulation it is impossible to state. It is probable, however, 
that the spinose end of the spheroidal body is thrust out of the genital 
pore pushing the tongue-like body before it. The large anterior branched 
pocket is probably simply a fold of the wall of the genital sinus which 
is straightened out when the spheroidal body is thrust forward. The 
tongue-like body is a muscular sac which is probably pushed entirely 
out of the genital pore during copulation and evaginated: it seems to 
me probable that in this condition it may receive the end of the spheroi- 
dal body of the other copulating individual. 
Hardly less remarkable than the structure of the genital sinus is 
that of the vas deferens (fig. 3). The two vasa efferentia come together 
immediately in front of the ovary to form this organ, which is made up 
largely of two enormous vesiculae seminales. The hindermost of these 
(fig. 3, 2) is the smaller of the two and is a thin-walled sac about 0,41 mm 
long and 0,154 mm in diameter. Its walls are muscular and have a 
thickness of 0,0045 mm. The forward end of this structure turns to- 
wards the right side of the body (fig. 1, 8) and then bends on itself and 
passes into the anterior vesicula seminalis (fig. 1, 7; fig. 3, 3). This 
~ structure is about 0,72 mm long and 0,21 mm in diameter and has walls 
of enormous thickness (0,04 mm) which are composed entirely of circular 
muscle-fibres (fig. 4): it undoubtedly acts as an ejaculatory apparatus. 
The anterior end of the vas deferens is a narrow tube (fig. 3) 
0,1 mm long and 0,03 mm in diameter, the walls of which are composed 
of outer longitudinal and inner circular fibres. It is separated from 
the vesicula seminalis by a circular fold of its inner surface (fig. 2, 15: 
fig. 3, 5) which leaves a very small communication between the two 
structures and probably acts as a valve between them. The anterior 
end forms a papilla-like prolongation (fig. 2, 14; fig. 3, 4) which has a 
minute lumen and projects into the common genital duct. No cirrus or 
cirrus-sac are present. 
The terminal portion of the uterus forms a muscular metraterm 
with a length of about 0,1 mm (fig. 2, 10). The common genital duct 
has a length of about 0,15 mm and opens into the cavity of the tongue- 
like body (fig. 2, 9). 
10* 
