NEPHRIDIAL TISSUES 



347 



regions of the upper, " narrow " part of the 

 earthworm's nephridial tubule. One part 

 ciliated. X 870. 



according to Benham, into five regions: (i) the narrow preseptal tube; 

 (2) " the very long but narrow tube 

 in continuity with the preseptal 

 tube" ; (3) "the short, brownish, cili- 

 ated, middle tube"; (4) "the wide 

 muscular tube or duct which opens 

 to the exterior." Each of these ex- 

 cept the preseptal tubule and the 

 short, brownish, middle tubule is 

 thrown into a loop. The latter tu- 

 bule communicates with the wide, 



large tubule by means of a distended Fm ^ __ A transverse section through two 

 part of the nephridial wall. This 

 distended region is histologically dif- 

 ferentiated from both the middle, 

 brownish tubule, and the wide, large tubule. This has been named the 



ampulla by Gegenbauer. 



Two rows of cilia arranged 

 in a slight spiral are found in 

 the preseptal tubule ; these cilia 

 continue into the first part of the 

 very long, narrow tubule, and 

 occur at other points in this lat- 

 ter tubule. The middle, brown- 

 ish tubule has also two rows of 



FIG. 308. A transverse section of the brown region cilia throughout its COUrSC. The 

 [the earthworm's nephridial tubule. X 870. cytoplasm of the long> nam)w 



tubule is finely granular. The nuclei are oval and smaller than in 

 any other part of the ne- 

 phridium (Fig. 307). The 

 syncytium of the middle, 

 brownish tubule is char- 

 acterized by a heavy alve- 

 olar structure. The 

 alveoli are most numer- 

 ous near the lumen. 

 The cytoplasm is more 

 abundant and the oval 

 nuclei of this tubule are 



laro-pr than thn^p of thp FIG. 309. A transverse section of the " ampulla" of the 

 tne earthworm's renal tubule, ex., excretion particles. X 870. 



narrow tubule. The rows 



of cilia lie opposite each other in the lumen (Fig. 308). The wall of 



the "ampulla" is sharply marked off from that of the brownish, 



