THE LTFE-HTSTORY OF NUCULA DELPHINODONTA. 381 



in some places a very difficult matter. Near the outer end of 

 each kidney the cells are smaller^ and the lumen is more 

 easily traced. As the kidneys grow, they extend anteriorly 

 and crowd dorsally beneath the pericardium and heart. As 

 growth continues they become bent into loops, and numerous 

 side pouches are formed. 



Although much time has been spent in trying to find the 

 inner, pericardial openings of the kidneys, I have not suc- 

 ceeded in placing them. Cavities leading from the peri- 

 cardium have frequently been traced nearly to the kidneys, 

 but the vacuolated condition of the cells that compose their 

 walls makes it very difficult to trace cavities with accuracy. 

 I have no reason to suppose that the pericardial openings do 

 not exist. I have simply been unable to find them. 



In the adult, the ducts of the genital organs pass close to 

 the lateral extremities of the pericardium. Near its end each 

 duct turns toward the median line, meets the outer end of the 

 kidney on the same side of the body, and opens with it into 

 the mantle chamber. This connection is easy to demonstrate. 

 Whether the genital ducts also communicate with the peri- 

 cardium, or with the inner ends of the kidneys, I am not 

 prepared to say. 



Genital Organs. 



The genital organs appear after the animal has become 

 adult in most other respects. Each genital organ consists, 

 at first, of a short and rather narrow tube that lies close to 

 the pericardium, for the most part in contact with it. 

 Whether this tube originates from the pericardium, or 

 whether it is formed in some other way, has not been deter- 

 mined. The genital organs grow rapidly, and extend ante- 

 riorly and dorsally over and among the lobules of the liver, 

 which are now very numerous. Soon the eggs and sperm 

 begin to be formed, and the sexes can be distinguished. The 

 eggs are few in number, but they are large and brown. The 

 sperm are very numerous, of moderate size, and pale yellow. 



