292 
A, G. BOURNE. 
needle-like crystals (fig. 11), which are also found in great 
abundance in the vesicle. 
The VESICLE DUCT is a tube 4-^ inch in diameter, with 
thin walls, formed by numerous cells, several cells surround- 
ing the lumen of the tube. It plunges into the substance 
of the anterior limb of the gland and assumes a different 
character. Henceforth I call it the central duct. 
The central duct is circular in transverse section, varies from 
aio lo ToVo ii^ch in diameter, and is lined by a very strongly- 
marked structureless cuticle, which has a radiating fibrous 
periphery, the fibrous irregular radii passing into the sub- 
stance of the nephridial cells which surround the duct, and 
also passing hetween them, where it becomes the proper 
cuticle of the cells (see figs. 7 and 18, c. d.). The central 
duct takes a course in the centre of the mass of cells w^hich 
constitute the lobes of the gland, and so far from being laby- 
rinthine, is entirely simple and unbranched, excepting at one 
point where it gives off a lateral offshoot similar to itself. 
Previous observers appear not to have distinguished be- 
tween this central duct, which is the direct continuation of 
the vesicle duct, and the immense plexus of ductules, to 
be described below, which excavate the cells surrounding the 
central duct, but which most assuredly are not ramifications 
of the central duct, and which I hav6 not been able definitely 
to trace into communication with it at any point, though I 
consider it possible that such a communication may exist at 
some one or possibly two points which have eluded my con- 
stant and very careful search. 
The central duct at its origin from the vesicle duct turns 
upwards (to the right in the figure) and traverses the arch 
of the main lobe, where it is surrounded by the peculiar 
nephridial gland-cells, which are in parts two or three rows 
deep. It descends in the posterior limb of the main lobe 
and passes on into the apical lobe. 
At that point of the posterior limb where the apical and 
main lobes are joined there is a constriction of the whole 
gland, and a sudden and marked change in the character of 
the nephridial cells. This sudden change has no effect at 
all upon the character of the central duct, which pursues its 
course along the axis of the apical lobe, arriving at last at 
the recurved apex of that lobe, where it rests upon the root 
of the testis lobe (see Plate XXIV, fig. 1). At the same 
time, although the central duct passes across the junction of 
main and apical lobes without any change, it gives off a 
branch — similar in character to itself — as soon as it has 
entered the ajdcal lobe. This branch 1 term the recurrent 
