DEVELOPMENT OF ACANTHODRILUS MULTIPORUS. 507 
out; this is the supra-intestinal vessel. Anteriorly about four 
pairs of hearts can be seen, and the ventral vessel is quite 
evident, running throughout the whole length of the body. 
The absence of any pigment in the integument is not so 
remarkable, since this species appears to have hardly any 
traces of integumental pigment at any time of its life. 
The nephridia have acquired their definitive form, with many 
external apertures in each segment. The mucous glands form 
a coiled mass of tubules lying on each side of the pharynx 
and oesophagus ; they are chiefly massed in the segment behind 
that which contains the pharynx: I presume, therefore, that, 
had I been able to examine a more complete series of embryos 
between these and those of stage C,a further fusion of the 
nephridia to form the mucous gland could have been traced. 
The aperture of this complex nephridial gland into the stomo- 
dzeum has moved still further back, still retaining its relation 
to the circumesophageal commissure, in front of which it 
opens, and beneath which it passes from the glandular coils. 
Fig. 9 shows the tube (Nephr.) which leads to the stomodeal 
orifice close to the latter and in front of the commissure (JV). 
I mentioned, in describing the nephridia of stage C, that the 
external aperture of the second pair of nephridia, which fuse 
with the first pair to form the mucous gland, still persist. In 
stage D there are numerous apertures by which the mucous 
gland opens on to the exterior; these commence upon the very 
first segment of the body. 
§ Anal Nephridia. 
The adult Acanthodrilus multiporus is, as I have 
recently pointed out (9), provided with anal nephridia 
which open into the hindermost section of the gut; there are 
also in the same segment integumental nephridiopores, and 
the tubes leading to the latter could be traced into connection 
with the tubes leading to the pores that communicate with the 
interior of the rectum. In these segments there are, moreover, 
numerous coelomic funnels, which seem to be wanting in the 
rest of the body of the adult, though, as I have already men- 
