8 E. RAY LANKESTER, ON THE 
canal are somewhat thick, transparent, and show a cellular 
structure; the cilia are large and vigorous, and the tube is 
long and frequently closely bent on itself, so as to give the 
appearance of a double tube. Gegenbaur* has described a 
more complicated arrangement in the earthworm, which I 
have not been able fully to confirm, the great difficulty 
of placing one of these tubes under examination in the micro- 
scope, without tearing or twisting 1t mto every variety of 
form, being one of the chief causes, no doubt, of this dis- 
crepancy. 
According to Gegenbaur, the segmental organ or ciliated 
canal of the earthworm is folded and refolded on itself in 
such a manner as to produce four canals of different dimen- 
sions running parallel to one another, the diameter of that 
which belongs to the end of the canal nearest to its external 
aperture being much greater than that of the others. The 
whole of the canal thus bent and complicated is held together 
by a membrane, on the surface of which ramify very numerous 
blood-vessels, derived from the abundant capillaries of the 
diaphragm-muscle. In fig. 4 is drawn a ciliated canal 
from one of the terminal posterior segments of a large earth- 
worm. The canal appeared to be folded on itself once, and 
to increase much in size towards its external termination, 
the walls increasing in thickness rather than the calibre of 
the canal becoming enlarged, whilst towards its interior ter- 
mination the tube was very much smaller, and its walls 
remarkably thin, the interior being freely ciliated. The 
expanded termination, for which no name is at present in use 
in this country, possesses a structure of conspicuous hexagonal 
cells, with distinct nuclei, the surface being densely fringed 
with cilia, M. D’Udekem has proposed the name “ entonnoir 
vibratile ” for the homologue of this expanded portion of the 
tube, and perhaps the name “ ciliated inductor” may be 
found a convenient though free translation of this term. The 
network of vessels with which the ciliated canals are connected 
is described by Gegenbaur, as also by Dr. Williams, who 
has figured the anastomosing capillaries and their sacculi. 
If a small portion of one of the ciliated tubes be examined 
with a power of 200 diameters, the various arrangements 
of its parts shown in PL, fig. 2, will be seen. The greater 
part of the wall appears to be composed of the thick, granular 
tissue (a), which is bounded externally by a delicate struc- 
tureless membrane, and internally by an equally structureless 
layer produced at intervals into coarse cilia (6). On the 
surface of the tube, the blood-vessel (c) is disposed, giving 
* © Koll, and Siebold’s Zeitschrift,’ 1852. 
