238 PROCEEDINGS OF THE ACADEMY OF [1883. 



posterior wall of the pericardium. The folds that I have referred 

 to above are not represented here, as they do not affect the general 

 form of the organ. At the point h' the sacular portion passes into 

 the tubular portion. Os represents the opening of the organ 

 into the branchial chambei*. The arrow is given to show the 

 position of the animal as regards the kidney, the arrow pointing 

 toward the head. The kidney is drawn as if the observer were 

 viewing it through the external wall of the branchial chamber. 

 The little canal {t) which is seen in the anterior part of sacular 

 portion is the communication between the kidney and the peri- 

 cardium. The diagram (PI. X, fig. 10 a) is drawn from a complete 

 series of •transverse sections, by first drawing each section and 

 then projecting it by measurement to surveyor's paper. 



The organ may be divided into two parts, which are in form 

 entirely different from one another. The first part — that is, that 

 part which lies next to the pericardium — I call the pericardial or 

 sacular portion (PL X, fig. 10 a) ; it is the largest and most active 

 portion of the kidnej^; it is fiattened from the side, so that the 

 greatest diameter is perpendicular to the animal. The walls, as 

 above stated, are thrown into longitudinal folds, which are much 

 deeper at the pericardial end than at the end where this part joins 

 the others ; at this point, in fact, it may be said not to exist, as 

 they gradually grow fainter until they disappear altogether. The 

 anterior end of this portion is very broad, and covers nearly the 

 whole posterior wall of the pericardium. This part, which runs 

 obliquely backwards and downwards, has an oval form on trans- 

 verse section which gradually becomes more circular as the folds 

 disappear and we approach the tubular portion. The length of 

 this first portion, in an average sized animal, is about 2-8 mm. ;* 

 the greatest diameter, TO mm. ; and breadth, 0*3 mm. 



In tlie posterior wall of the pericardium is seen a small funnel- 

 shaped opening (PI. X, fig. 3 inf)^ which is lined with long cilia; 

 this opening leads into a fine tube ; this tube lies in contact with 

 the internal wall of the sacular portion of the kidney for a short 

 distance, and then opens into it. Here we have, without doubt, 

 a direct communication between the pericardium and the kidney. 



This small tube may be divided into two parts, histologically 

 different from one another, and the point where this division takes 



1 All measurements are taken from an animal of average size, which 

 measured 7 "4 mm. in length. 



