372 J. T. CUNNINGHAM. 



a series of sections the end opening into the latter is first met 

 with when the series begins from the anterior end of the pre- 

 pared piece of tissue. The actual opening of the canal into the 

 main cavity of each kidney is seen in such sections with the in- 

 jection in the canal and in the aperture. A triangular piece of 

 tissue is seen before each opening, which lower down joins 

 with the tissue of the projection, which contains the canal, 

 and therefore forms a sort of valve open towards the kidney 

 and closed towards the pericardium. The part of the canal in 

 the immediate neighbourhood of the aperture into the kidney 

 is lined by cellular epithelium, which consists, apparently, in 

 some places of more than one layer of cells. There are in 

 many sections indications that this epithelium is ciliated, but 

 whether it is so or not I could not definitely determine. 

 Towards the part of the canal communicating with the peri- 

 cardium the epithelium disappears ; it may pass into a fiat 

 epithelium lining the whole interior of the pericardium, but my 

 sections do not show this clearly. 



I have been able to discover and study these canals in series 

 of sections prepared without injection, and in these the epi- 

 thelium is seen much more clearly. 



With regard to the position of these canals, it is to be ob- 

 served that the projections towards the cavities of the kidneys, 

 through which they run, lie close to the external surface of the 

 body, that surface which forms part of the floor of the mantle 

 cavity ; this is especially true of ihe canal belonging to the left 

 renal organ. In the second place, they are not far distant 

 from the external apertures of the kidneys, as is shown by the 

 fact of the sections in which they are sefen including a portion 

 of the mantle cavity. 



It is difficult to understand how it can have come about 

 that the right kidney of Patella communicates with the peri- 

 cardium by passing under the intestine instead of over it, unless 

 the intestine at one time passed through the pericardium ; in 

 this case ii could in passing out again during ancestral history, 

 and becoming separated from the pericardium, have passed 

 between the two openings of the kidneys ; but if the pericar- 



