370 J. T. CUNNINGHAM. 



to one another. My investigations were commenced in the 

 Zoological Laboratory of University College, London, under 

 the supervision of Professor Lankester, and were subsequently 

 completed at Naples in the winter 1882-83. 



I injected several specimens of Patella vulgata from the 

 south coast of England with gelatine solution coloured with 

 Berlin blue by means of a fine-pointed pipette inserted into the 

 pericardium of the animal in the fresh state, and after harden- 

 ing I cut out the piece to be examined, stained it whole, and 

 cut it embedded in paraffin. I frequently found the injection 

 in the cavities of both kidneys, and soon became convinced 

 that each kidney had a separate communication with the peri- 

 cardium ; but the difficulty of getting complete series of sections 

 with the tissues well preserved, in which the channels of com- 

 lUnication could be satisfactorily traced by means of the injec- 

 tion, was so great that I was unable to discover the exact 

 character and relation of the canals leading from the pericardium 

 to the ca»vity of the kidneys. At the Naples Zoological Station 

 I have used for injection simply the cold solution of Berlin blue 

 in water, which has many advantages over the gelatine solution ; 

 it penetrates more easily, and is seen in sections as a blue line 

 along the sides of the cavities which it has reached, while the 

 gelatine has the two disadvantages of solidifying before the in- 

 jection is complete, and contracting during the process of har- 

 dening. After many trials I have succeeded in obtaining 

 complete series of sections from injected and uninjected speci- 

 mens, in which the two canals of communication can be traced 

 through their whole length. 



The species of Patella which I have used at Naples, and 

 which is most common there, is P. coerulea; its shell is much 

 flatter than the P. vulgata of the English coast, and it does 

 not attain such a large size ; but I have found no differences 

 between the organs of the two species. 



When a Patella is removed from its shell in the fresh state 

 the dorsal surface appears of a deep black colour, which is due 

 to the presence of pigment in the superficial epithelial cells. 

 This pigment can easily be washed oflf. When this is done, and 



