THE LEECHES OF JAPAN. 339 
half the somite. In a transverse direction the vesicle has 
about the same extent, so that its capacity is well nigh equal to 
that of the undistended cecum. 
It isapparent then that the vesicle here represents a bladder- 
like reservoir, the capacity of which, relatively speaking, must 
at the lowest estimate be more than double that of the corre- 
sponding part in the Medicinal Leech. I have not discovered 
any cilia in the vesicle, but I am not prepared to say that they 
are wanting. 
The efferent duct is composed of two distinct portions; the 
lumen of the inner portion is much larger than that of the 
outer, and is lined with an epithelium quite like that of the 
vesicle ; the outer portion, which is nearly equal in length to 
the inner, is lined by an involution of the epidermis, and is 
supplied with both ring and radial muscle-fibres. The inner 
portion is furnished with ring fibres alone, which are multiplied 
in number at its junction with the vesicle, so as to form a 
powerful sphincter. The course of the comparatively long 
efferent duct is nearly at right angles to the axis of the body, 
the inner portion being nearly horizontal, and the outer in- 
clining a little upward to reach the margin. 
The glandular part of the nephridium is somewhat larger 
relatively than in Hirudo, lies in front of the vesicle, and opens 
into it by a funnel-shaped orifice. The “ vesicle duct’’ passes 
directly into the smaller “central duct,” which, after perforating 
a convoluted chain of shells, enters the more massive portion 
in which the cells are arranged radially. According to Bourne, 
the vesicle duct in Hirudo is “formed by numerous cells, 
several cells surrounding the lumen of the tube.” In the case 
of the Land Leech the vesicle duct is formed of a single chain 
of cylindrical cells, each cell entirely surrounding the lumen. 
The chief difference then between this duct and the adjoining 
portion of the central duct is its greater lumen. 
It remains to find some explanation for the extraordinary 
size of the nephridial vesicles. It is now generally admitted 
that the nephridia are renal organs; and this view of their 
function has tended to bring into discredit the idea that the 
