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. 



tively 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. The wall 

 of this collar is highly 

 modified and in being 

 less soluble in caustic 

 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 



mav lie beVOnd the collar 



-11 f i 



into the lumen of the 

 nephridial tubule. A supporting membrane is found rising from 

 the nephridial tubule and giving off external flagella which probably 



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

 lalia. (After FACE.) 



