Note on the structiire and relations of the kidney in Aplysia. 423 



parent membrane. To examine the siirface of the kidney which lies in 

 the wall of the branchial cavity, the animai is turued slightly on its left 

 side and the mantle fold drawn to the left as far as possible so as to 

 expose the cavity completely. The branchial cavity is divided into two 

 eompartments by the gill which is in the form of a triangle with the 

 apex curved towards the posterior end of the animai and attached con- 

 tinuously along the base. This line of attachment runs across the sur- 

 face of the kidney, a small part of which is seen above the gill and a 

 larger part below. The external opening of the kidney is a small aper- 

 ture below the line of attachment of the gill, close to the latter and near 

 its posterior extremity. In the living animai the opening is seen to ex- 

 pand and contract. A better view of the branchial cavity is seen, when 

 the gill is cut away near its base as in fig. 2 , where hr represents the 

 remains of the gill so removed. In the same figure the so called siphon 

 or semitubular Prolongation of the mantle is seen at si\ on the inner 

 surface of the siphon, near the angle where its lower border joins the 

 body is the anus , cm. The lower side of the anterior end of the gill- 

 attachment carries the olfactory organ of Spengel, ol: the opening of 

 the kidney is shown at eo : the area occupied by the » poison glands « 

 pg is on a level with the anterior end of the gill, inside the line of ori- 

 gin of the right epipodium and in front and to the left of these are the 

 genital opening, go. and the commencement of the seminai groove sg. 



All the surfaces of the kidney have now been described except that 

 which is turned towards the internal organs of the body : this is quite 

 fiat and lies upon the rounded mass formed by the large liver and the 

 convolutions of the intestine to which it is attached. This internal sur- 

 face extends from the lower boundary line of the surface belonging to 

 the branchial cavity, to the outer boundary line of the dorsal surface, 

 and as the branchial cavity is very deep, the internal surface of the kid- 

 ney is of slight extent. 



To determine the position and nature of the renopericardial opening, 

 which cannot be done by mere dissection , I injected the pericardium 

 with a cold Solution of Berlin blue in weak oxalic acid , in the fresh 

 animai. The injection ran down into the kidney along a line parallel 

 and close to the attachment of the gill, and its course could be seen when 

 the branchial cavity was examined. I then dissected out the kidney 

 hardened it and cut a series of sections perpendicular to the surface 

 bordering the pericardium and parallel to the direction taken by the 

 injection. This method is excellent for tracing similar passages, as the 

 injection remains attached to the surfaces it has reached, and does not 



Mittheilnngen a. d. Zoolog. Station zu Neapel. Bd. IV. 28 



