NEPHRIDIAL TISSUES 



347 



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 

 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 

 of the earthworm's nephridial tubule. X 870. cytoplasm Q f the long) nam)w 



FIG. 307. A transverse section through two 

 regions of the upper, " narrow " part of the 

 earthworm's nephridial tubule. One part 

 ciliated. X 870. 



tubule is finely granular, 

 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 

 larger than those of the 

 narrow tubule. The rows 



The nuclei are oval and smaller than in 



FIG. 309. A transverse section of the "ampulla" of the 

 earthworm's renal tubule, ex., excretion particles, x 870. 



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, 



