226 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



aperture through which the renal excretion is discharged. 

 (Fig. 21, ren. p.) It lies in the wall of the pallial cavity at 

 the root of the ctenidium. Its walls a-re muscular. There is 

 no ureter, but the renal sac empties its excretion directly 

 through the renal pore. The reno-pericardial duct connects 

 the cavities of the renal sac and pericardium, and is thus a 

 means of communication between the renal and pericardial 

 portions of the coelom. It brings about a secondary connection 

 between the pericardium and the exterior. The duct is not 

 visible to the naked eye and is difficult to demonstrate by 

 injection in Aplysia punctata, as Cunningham was able to do 

 in the larger Mediterranean species. Sections, however, show 

 that the duct is situated close to the entrance of the efferent 

 branchial vessel into the auricle. 



Internally the kidney consists of fairly regular parallel 

 lamellae, which are pendent from its dorsal surface and are 

 held in place by fibrous bands arising from the floor of the 

 renal sac. The lamellae sometimes branch. They run 

 obliquely across the cavity. A single layer of non- ciliated 

 cells forms the wall of each side of the lamella, and between 

 two walls is a blood sinus. Blood enters the kidney by a 

 dorsally placed afferent renal sinus, collecting from the left 

 anterior portion of the ventral abdominal sinus, and to a 

 lesser extent from the left body wall and left parapodium. 

 Small sinuses enter the right anterior border of the gland from 

 the mantle from the part roofing in the kidney. These sinuses 

 branch repeatedly over the surface of the renal sac, lying in 

 channels excavated on its upper surface. The blood passes 

 through the lamellae to collect again in a large sinus, the 

 efferent renal sinus, on the floor of the gland. The efferent 

 renal vessel leaves the ventral side of the kidney on its right 

 side, and discharges into the efferent branchial vessel just as 

 the latter enters the auricle. (Vide Blood Vascular System.) 



The kidney is innervated from the branchial ganglion. 

 (Fig. 16, ren. n.) 



