626 NOTES ON PROSOBRANCHIATA, 



revised edition (1871) is incorrectly figured by Wilton in Wood- 

 ward's 'Manual'; my figure (fig. 1) supplies this deficiency. I 

 have counted over three hundred rows of teeth on the ribbon. 



The nephridiuni (figs. 1, 2, 3, -i, neph.) is situated just behind 

 the end of the pallial cavity, of which it, in part, forms the 

 posterior boundary. It is slightly more on the left hand side 

 than on the right. In the figures it has been detached from the 

 liver, and laid back on the right hand side. The reno-pallial 

 orifice is on the left hand side; its position is shown in figure 

 (tig. 1, r.h.o.). The natural position of the nephridium is shown 

 in the figures by the dotted line, but the line of the anterior 

 attachment is shown only on tig. 4, by the double dotted line; 

 from this it will be seen that there is a pocket of the organ over- 

 lying the pericardium. The reno-pericardial orifice is very small; 

 its position is under the pocket just mentioned (fig. 4, r.p.o.). 



Circulatory system (tig. 2) : — The heart (fig. 2, heart; tig. 5) lies 

 in the pericardium, immediately behind the ctenidium and in 

 front of the nephridium, a pocket of which, as already mentioned, 

 overlies it. It consists of a thin- walled auricle (fig. 5, aur. ), well 

 divided from a larger and thick-walled ventricle (fig. 5, vent.). 

 The arterial system consists of a very short aortic trunk, which 

 gives rise to the anterior and posterior aortae. The former 

 (fig. 2, ant.aor.) enters the body cavity alongside and slightly below 

 the oesophagus, underneath which it passes, apparently without 

 giving off any branches till the centre of the crop is reached, 

 where a small branch, which bifurcates at once on the underside of 

 that organ is to be seen. Continuing forward it suddenly 

 diminishes just posterior to the pedal commissures and ganglia; 

 the main branch here enters the foot. A smaller branch continues 

 forward and supplies the head and buccal mass. The posterior 

 aorta (aorta visceralis) almost at its inception, sends a branch 

 to supply the liver, under the nephridium (fig. 2, a.). Further 

 back another and rather larger branch arises which supplies 

 the rectum, uterus, and right side of the mantle (tig. 2, b.). 

 From this second branch the aorta passes through the liver, 

 so far as I can ascertain, without branching till it reaches the 



