534 CEESSWELL SHEAKEE. 



undoubtedly take a great part. Their action is probably 

 selective. If we take the average length of a solenocyte tube 

 to be one hundredth of a millimetre, and allow sixty soleno- 

 cytes for each of the eight nephridia, a number very much 

 below their number in the case of the second, third, and 

 fourth pairs of nephridia, we get a total length of 4'8 mm. 

 of solenocytes for the whole animal, which represents a con- 

 siderable area for osmotic exchange iu an animal whose total 

 length is under one millimetre. It is thus evident that a 

 considerable amount of fluid could be rapidly excreted from 

 the body-cavity by means of the solenocyte tubes. The 

 nephridial canals, however, never show the presence of fluid 

 passing down their interior, and the process of excretion is 

 possibly a very slow one. 



III. The Second Nephridium. 



The second pair of nephridia occupy the corners of the 

 body-cavity space opposite the anterior end of the stomach 

 (figs. 3 and 4). Into the triangular ends of these spaces 

 their solenocytes project from the ends of the canal portions 

 of the nephridia. The solenocytes are more numerous than 

 in the case of the first nephridium, and, in fact, the whole 

 nephridium is better developed. Numerous grannies are 

 seen, as in the case of the first nephridium, frequently 

 lodging among the solenocytes. The end of the canal 

 towards the body-cavity in this case is distinctly closed, its 

 walls being marked out by dense masses of deep orange 

 pigment arranged in irregular masses along the first part 

 of its course. The granules in the wall are large and refrac- 

 tive, and render the nephridium readily visible even when 

 the flagella in its interior are not in motion. About the 

 middle of the testis this portion of the nephridium graduates 

 into the third part at the point at which the canal turns to 

 run through the testis in a ventral direction (see fig. 4). The 

 canal then continues its course ventral to the testis and 

 slightly backwards into the next segment, to terminate iu 



