234 Scientific Proceedings, Royal Dublin Society. 



latter opens to the exterior — a position which is certainly at vari- 

 ance with the normal arrangement in moUuscan or other excretory 

 organs. 



I have made at least two series of transverse sections through 

 Trachydermon ruber (Linn.), from Norway/ and find that they cor- 

 roborate Sedgwick's account in every essential point. 



An examination of Plate X., figures 5-8, will render the sub- 

 ject quite clear. These are consecutive sections, one side of the 

 animal only being drawn. I should add that the sections are a little 

 oblique. Owing to the animals not being well preserved, I am 

 unable to give histological details ; but, in both the animals, the 

 histological characters of the internal and external ducts are suf- 

 ficiently well marked to prevent any mistake. 



In figure 5 we have a section of the recurrent or pericardial 

 duct of the kidney [p. d.) attached to the ventral wall of the peri- 

 cardium ; and external to this is the large thin- walled kidney- 

 body [Ti. h.), the " bladder-like structure " of Sedgwick, with its 

 glandular cseca on the lateral wall of the pericardial chamber ; and 

 opening into it is the cut end of a ciliated tube (r. p. d.). In the 

 succeeding sections (Plate XI., figures 6, 7) this tube is seen to 

 pass into the pericardial duct of the kidney, and is, in fact, a special 

 recmwed portion of that duct. 



On the other hand, figures 7, 8, and the succeeding two sections, 

 show the kidney-body passing outwardly through the muscular 

 wall of the body, and curving over the lateral nerve- cord and 

 below the branchial vein, eventually to open on the exterior mesial 

 to the gill row. 



The pericardial orifice of the kidney opens about the level of 

 the outer communication of the auricles with the ventricle ; and 

 the external aperture is only a short distance posterior to it. 



At present the case stands thus : Sedgwick says that there is a 

 pericardial orifice in Ch. discrepans and Ch. cancellatus. Haller 

 denies it in Ch. siculus (Gray) and Ch. cajetanus. Van Bemmelen 

 has found it in Ch. marmoreus (Fabr.), Ch. marginatus, and Chitonel- 

 hisfasciatus. I now describe it in Ch. ruber (Linn.). From indica- 



1 These specimens of Ch. ruber from the Natural History Museum were collected by 

 P. Chr. Asbjornsen of Norway, and were kindly placed at my disposal by my friend 

 Mr. A. G. More, the Curator of the Museum. 



