370 Ralph S. Lillie 



minute grauules to lai'ge rounded masses of half the dìaraeter of the 

 celi; they are of very variable occiirrence, at times ver}- numerous 

 aud at other times almost entirely absent. They appareutly repre- 

 sent the final stage of the excretory products immediately before 

 their extriisiou into the lumen of the nepbridium. Frequently bodies 

 of precisely similar appearance are fouud iu the lumen immediately 

 without the celi wall and apparently stili adhering to the latter. 

 Such bodies bave evidently recently been extruded. The indications 

 are therefore that the black granules do not represeut the final 

 stage of the excretory products ; but tliat the latter undergo a further 

 chemical transformation in the outer portion of the cells before being 

 cast out into the lumen. 



The outer rounded margin of the celi usually projects into the 

 lumen of the nepbridium and bears flagella. The number of 

 flagella is not, however, constantly one to each celi, as sometimes 

 hcld; a single celi may frequently bear a tuft composed of several 

 flagella. The projection of the cell-body into the lumen is in 

 general less prominent in cells that contain relatively few excretory 

 grauules. 



The terminal vesicle is also lined internally by excretory cells 

 of the same general character as the above. Between the bases 

 of the epithelial cells aud the investing connective tissue layer, is 

 situated a strong network of muscle fibres whose Strands divide 

 the surface of the vesicle into the hemispherical elevated areas above 

 described. In other respects, the histological structure of the vesicle 

 is similar to that of the tubulär region. The muscular network is 

 derived, in a manner to be later described, from the longitudinal 

 fibres of the body-wall and is continuous with these. 



A comparison of the excretory cells of the adult nepbridium 

 with those of earlier stages shows various points of agreement and 

 disagreement. Fig. 6, Piate TI shows a longitudinal section through 

 the wall of the nepbridium of a larva of 5 — (j mm. The cells, it 

 will be observed, are much shorter and broader than those of the 

 adult ne)»hridium and contain fewer granules, which furtbermore fail 

 to show the definitencss of distribution found in adult individuala. 

 In the general characteristics of the i)rotoplasm, its vacuolation, and 

 its greater density at the base of the celi, the larvai excretory cells 

 agree Avith the adult; and the nuclei are of almost precisely similar 

 size and appearance, even to the presence in each of a conspicuoufl 

 nucleolus which almost always contains a well defined vacuole. The 



