294 
A. G. BOURNE. 
V. — The Ductules and Nephridial Cells. 
When I commenced the study of the Leech’s nephridium 
I regarded the numerous minute passages which give the 
labyrinthine character to that organ noted by Gegenbaur as 
necessarily only branches and ramifications of the system of 
the central duct. Nevertheless, in none of the many hundred 
sections of the nephridium which I have examined have I 
been able to find a single instance of a ductule opening into 
the central duct or into its recurrent branch. 
The ductules of the Leech's nephridium are passages lined 
by a firm resistant cuticle, which excavate the secreting cells 
of that organ in such a way that every individual cell is 
completely bored through by such a passage (the grey net- 
work in fig. 1). Further, the passages differ very much in 
calibre in the different lobes of the nephridium, and not only 
that, but differ further from one another in being in some 
cells simple traversing passages (a. l. in fig. 13), whilst in 
other cells they are hranched within the cell (figs. 5, 6, T). 
Further still, the branches may be all passages lead- 
ing into corresponding passages in neighbouring cells (fig. 3), 
or most of the branches may be ccecal, in which case they are 
often exceedingly minute (fig. 5). ^ 
Nothing equalling in complexity the system of intra- 
cellular passages or ductules of the nephridial cells of Hirudo 
has hitherto been described by previous writers on that 
animal, nor has anything quite parallel been described in 
any other cell-structure, so that the facts which I have 
ascertained with regard to these ductules in the Leech’s 
nephridium have a certain histological interest of a general 
character. 
It was, I believe, first pointed out by Claparede, who for 
the first time made sections of the nephridium of the earth- 
worm, that the tube of which that organ consists is built up 
by a single series of cells (throughout the greater part of its 
length), and that these cells are simply bored thrpugh by 
the duct or lumen of the tube. Each cell accordingly has 
the form of a drainpipe. A similar structure has now been 
recognised in the embryonic nephridia of larval Pulmo- 
Gasteropods (Rabl), and is clearly enough characteristic of 
nephridia of a certain grade of elaboration.^ At the same 
^ It is suggested by Professor Lankester tliat the structure in question 
probably points to the phyletic origin of the nephridia from simple uni- 
cellular glands, rather than from pockets or invaginated pouches of the 
eiiidermis consisting of many cells surrounding a cavity. A nephridial tube, 
consisting of a lineal series of perforated cells, is simply a unicellular 
