62 ART. 4. Ni YATSU : 



its anterior two thirds the organ is made up of two kinds of 

 cells ; the tube formed of large glandular cells constituting the 

 axis (ax.), and smaller cells forming a sheath (sth.) around the 

 above mentioned axial tube. The axis is identical with the cell 

 tube found at the preceding stage ; the cells are entirely filled with 

 excretion granules and, in life as well as in preserved specimens, 

 they look highly refractile. Nuclei are inconspicuous, having less 

 affinity for stains. The canal in the tube is hardly visible in this 

 section, but in others it appears as a tolerably wide caual (PL 

 VII., Fig. 110). The sheath is a layer of mesoblast cells, which 

 are almost cubical or exceedingly rounded toward the body cavity. 

 In surface view accordingly these cells give a warty appearance 

 to the nephridium. The nuclei are comparatively large, spherical, 

 and have a great affinity for stains. It is certain that these 

 mesoblast cells have been derived from the peritoneum, as the 

 nephridium shifted away from the body wall, and that they 

 increased in number by subsequent division. 



The nephridium in its posterior one third (Wood-cut p. 58, 

 PI. VIL, Fig. 109, and PL VIII., Figs. 133, 134, fn.) consists 

 of peculiar mesoblast cells, forming a funnel closed anteriorly but 

 open dorsally at the posterior end. The cells are arranged 

 epithelially and the nuclei stain intensely, as in those of the 

 sheath. Posteriorly these cells become a thin plate which forms 

 a part of the ileo-parietal band (vide p. 58.). The cells of the 

 ileo-parietal band and of the tube-part may contribute to the 

 formation of the funnel, but I have no evidence as to its origin. 

 At the end of the 9 p. c. stage the funnel does not yet open 

 anteriorly. 



By study of transverse sections the relation just referred to 

 will be more clearly understood. The nephridial tube which 



