BURNE‘: RENAL ORGANS OF NUCULA NUCLEUS. 301 
in Yoldia limatula the genital duct is described and figured by Drew 
as opening into the organ of Bojanus close to its external orifice, 
as he says it also does in Nucula proxima and LN. delphinodonta ; 
although in the latter case he is not prepared to say that it has not 
also a connection with either the pericardium, or the reno-pericardiac 
duct. In Leda sulcata, L. pella, and Malletia Chilensis, Stempell 
describes the passage of the genital duct into the organ of Bojanus 
close to its external opening, but notes in addition in Leda sulcata 
an open communication between the pericardiac arm of the kidney 
(close to the pericardium) and the uro-genital cloaca formed by the 
union of the genital duct and ureter. In JMalletia this ‘ gono- 
pericardiac’ duct is represented by a solid cord. Pelseneer, in 
a second paper,! revises his former description of these parts in Wueula, 
Leda, and Solenomya, and states that in these forms, as well as in 
Yoldia hyperborea, the genital duct opens into the pericardiac arm 
of the kidney, where it passes into the reno-pericardiac duct, but that 
a secondary connection leads directly from this point of confluence of 
the two organs to the external renal opening—a statement that may 
well be a reverse interpretation of a condition similar to that recorded 
by Stempell for Leda. 
In face of these somewhat conflicting accounts, further investigation 
into the relationship between the genital ducts and the organ of 
Bojanus in these genera is much needed. But, as may be gathered 
from the want of unanimity in the descriptions of even the same 
species, these parts, from their delicacy and close apposition, are 
extremely difficult to disentangle with any certainty except in really 
well-preserved material. Amongst several indifferently preserved 
series of sections of Nucula nucleus, | was fortunate enough to get one 
in exceptionally good condition, so that I am in a position to add yet 
another description of the anatomy of these organs, which, so far as 
the specimen is concerned, should be reliable. 
In any transverse section, taken close in front of the nephrostomes, 
the longitudinally pleated genital duct (Pl. X, Figs. 1 and 2, od.)—in 
this particular instance the oviduct—is found lying on either side 
below the pericardium, between the body-wall and the excurrent arm 
of the kidney and above the cerebro-visceral connective. From this 
level it can be traced backwards, below and to the outer side of the 
reno-pericardiac duct, the latter being tightly wedged in between it 
and the excurrent arm of the organ of Bojanus. The duct now turns 
‘inwards towards the mesial plane, meets the antero-lateral wall of the 
ureter above the cerebro-visceral connective, and opens into it, 
converting the distal part of the ureter into a uro-genital cloaca 
(Fig. 2, wg.c.). The reno-pericardiac duct, as just stated, lies for the 
first part of its course upon the dorsal surface of the oviduct. As 
it makes its way towards the deep surface of the ureter to pass 
behind it to the pericardiac arm of the kidney, it occupies the 
angle formed by the union of the genital duct and the ureter, and 
1 Pelseneer, Recherches Moll. archaiques: Mém. Cour. Acad. Roy. Belgique, t. lvii 
(1899 [i.e. 1901]), p. 62. 
