DEVELOPMENT OF ACANTHODRILUS MULTIPORUS. 5035 
which is placed on the anterior side of the intersegmental 
septum, behind which the nephridium lies. The funnel is 
ciliated, and the nephridium, where it communicates with it, 
has a remarkably wide lumen, and is ciliated. The funnel lies 
close to the nerve-cord, but the external apertures of the 
nephridia are more dorsal in position ; they open in the neigh- 
bourhood of the lateral setze. 
Fig. 21 represents a single nephridium, which happened to 
be displayed in a fortunate section for nearly the whole of its 
course. The nephridia are present to the number of a single 
pair per segment, but the anterior pair (the “ mucous glands ” 
of the adult worm) occupy two segments. 
These, however, like the following ones, have a single 
funnel, which is placed on the anterior side of a septum (see 
fig. 22), which seems to represent the septum dividing Segments 
1m and 111. In this region of the body, however, from the 
earliest stage the septa have not the regular arrangement that 
they have posteriorly. The first pair of nephridia open 
close to the stomodeal aperture; the funnels neces- 
sarily lie behind this point, hence from the very 
first this anterior pair of nephridia is anomalous, 
and so far unlike those which follow. It would be very 
interesting to ascertain whether this difference holds good 
from the first formation of the nephridia; unfortunately this 
is one of the many questions in the embryology of Acantho- 
drilus multiporus which I have no means of solving at 
present. 
Figs. 17 and 18 represent two successive sections which 
illustrate the position of a nephridium. In fig. 17 the external 
aperture is seen, which lies dorso-laterally ; in fig. 18 the 
funnel is shown. The first figure shows more of the anterior 
extremity of the body, owing to the somewhat awkward 
position in which the worm was embedded. The developing 
sete of Segments 11 and 111 belonging to one of the ventral 
pairs are seen on the left side (fig. 18); they fix the position of 
the funnel which is seen to lie between them on the anterior side 
of a septum. The enormously distended cavity which lies 
