NEPHRIDIAL TISSUES 



345 



FIG. 304. Transverse section of a renal tubule of a caddis 

 larva. The tubule is formed (in transverse section) of 

 two cells which, because of the alternation of their central 

 masses, show but one nucleus in any given cross section. 

 The distal surfaces of the cells, where they border on the 

 lumen, show a cuticular edge, x 550. 



lively small. In it excretion products are seen. The tubule is incased 

 in a membrana propria or basement membrane (Fig. 304). This gland is 

 a modified and invagi- 

 nated portion of the 

 intestinal epithelium. 



Eulalia viridis Miill., 

 according to Page's de- 

 scription, possesses ne- 

 phridia which are more 

 complex than those of 

 the flat-worm. The ne- 

 phridium has a conduct- 

 ing tubule. The lumen 

 of this tubule is intra- 

 cellular, and its wall is a 

 syncytium. These latter 

 features are frequently 

 met with in excretion 

 tissues. There are a 

 few scattered cilia in the 

 lumen. The nuclei are not frequent. The inner zone of cytoplasm is 

 extremely finely granular. The outer zone is marked by striae which 

 stain deeply. This nephridial tubule bears distally a row of solenocytes. 

 Each solenocyte is represented by a mass of cytoplasm which is fused 

 with the cytoplasm of its neighbor. The nucleus lies in this cytoplasmic 

 body. Each cytoplasmic mass gives off a collar which pierces the wall 



of the tubule to empty 

 into its lumen. 

 of this collar 

 modified and 

 less soluble 



potash than cytoplasm 

 shows a marked differen- 

 tiation. Its length is 

 twenty to twenty-five mi- 

 crons. It has a very small 

 lumen. Within this lumen 

 Fage describes a single, 

 slender flagellum which 

 may lie beyond the collar 

 into the lumen of the 

 nephridial tubule. A supporting membrane is found rising from 

 the nephridial tubule and giving off external flagella which probably 



The wall 



is highly 



in being 



in caustic 



FIG. 305. Inner end of a renal tubule of the worm, Eu- 

 lalia. (After FAGE.) 



