426 J- T. Cunningham 



presenta is shown in fig. 7«. The cells liere have a somewhat polygonal 

 shape due to mutuai pressure ; inside them are seen the brown or black 

 concretions, and occasionally the outline of part of one cell is seen 

 through another which lies over it. The shape and quantity of the 

 concretions varies in different cells : the most common form is that of 

 an aggregation of minute spherical molecules, which often show a trem- 

 bling motion, the Brownian movement; but occasionally a cell contains 

 a single large crystal, whose shape is a regulär pyramid with a Square 

 base (flg. 7 h and c) . When a little of the contents of the kidney is 

 pressed by gentle pressure from the external opening of the organ and 

 examined the material so obtained is found to consist of cells similar 

 to those in teased preparations of the renal tissue, and of debris derived 

 from such cells. The entire cells are often still connected together in 

 masses and groups as seen in fig. 8. 



I have not been able to find any ciliated cells in either sections or 

 teased preparations from the kidney of Aplysia, although the vesicular 

 renal cells containing concretions are ciliated in many Gasteropods e. g. 

 Patella : in this respect Aplysia agrees with Pleurobranchus according 

 to Lacaze - DüTHiERS ^ , with Tethys according to von Ihering 2, and 

 with Tritonia according to my own observations. 



The process of renal secretion evidently takes place as in other 

 Gasteropods, e. g. Patella and Tethys, by the development of a vesicle 

 in each epithelial cell as it matures and the escape of the cell, when the 

 vesicle is fully developed. The proper excretion of the organ consists in 

 the concretions and fluid contained in the vesicles. The escape of the 

 vesicular cells from the external opening, their loose attachment in 

 teased preparations, and the appearances to be seen in sections all point 

 clearly to this as the method of secretion ; but I have not followed out 

 completely either in sections or teased preparations the various stages 

 of development of the renal cells. 



Morphologically the kidney of Aplysia corresponds in its relations 

 to other organs , with the kidney of those Prosobranchia in which the 

 organ is single and with the left renal organ of Zeugobranchia and of 

 Patella : the external opening lies in front of the anus on the right side, 

 as would be the case in a typical Prosobranchiate e. g. Tritonium, if we 

 suppose the twisting, which has carried the gill, rectum and renal organ 

 to the anterior part of the dorsal surface , to be reversed to a certain 



1 Ann. Sei. Nat. 4th Ser. Vol. XI. 



2 Morph. Jahrbuch. Vol. 2. 



