STRUCTURE OP UROCHAETA AND DICHOGASTER. 243 
may be equally well interpreted on the view that we have here 
a rudiment of a primitive condition in which the nephridial 
system formed a continuous network, with many funnels and 
many external apertures in each segment. 
I shall now bring forward further evidence of the truth of 
this latter view. 
Perrier has referred to the presence in Perichaeta of a 
mass of glandular tubes in the anterior segments ; these were 
figured by him in P. Houlleti, and were at first erroneously 
regarded as connected with the alimentary canal. Later, they 
were correctly referred to the excretory system. M. Perrier 
remarks (22, p. 639) “that the segments (in Perichaeta) which 
contain these glands are usually filled by a thick yellow secre- 
tion, which the animal evacuates when annoyed.” This secre- 
tion must be expelled, M. Perrier thinks, by the dorsal pores, 
since he was unable to discover any excretory canal like that 
of Urochaeta. Now, Urochaeta is an extremely small 
worm, and an anatomist who lias proved himself sufficiently 
skilful, as M. Perrier has done, to dissect out the minute duct 
of the “mucous gland,” embedded as it is among the muscles 
of the pharynx, would hardly fail to trace the same duct, if it 
existed, in the comparatively large Perichaeta. By the study 
of transverse and — which are perhaps better for this purpose — 
longitudinal sections, I can quite confirm Perrier’s conclusion 
as to the absence of an excretory canal like that of Urochaeta. 
1 have, however, already (1) shown that the nephridia of these 
segments open on to the exterior by numerous pores, and that 
the nephridia of adjacent segments communicate through the 
septa; this at any rate applies to P. aspergillum. In the 
few first segments of the body of P. aspergillum (1) 
the nephridial system is enormously developed ; all the 
coelomic space available is closely packed with tubules. On 
dissection this part of the excretory system has, comparatively 
speaking, a solid appearance ; through the rest of the body the 
nephridia are by no means so conspicuous, and, indeed, they 
require a microscope for their demonstration. 
The massing of the nephridia in a few of the anterior seg- 
