346 



HISTOLOGY 





direct currents of the ccelomic fluid toward the solenocytes (Fig. 305); 



such solenocytes with long and powerful cilia have also been described 



by Goodrich ('oo) for Aste- 

 rope Candida Cam. The so- 

 lenocytes probably take up 

 waste materials from the 

 crelomic fluids. The wall of 

 the nephridial tubule has a 

 blood capillary supply. In 

 the worms the chief amount 

 of excretion products is 

 taken from blood by the 

 nephridial walls. This 

 rather complex type of ne- 

 phridium in modified forms 

 seems to be present in many 

 polychaetes. 



The nephridium of Syco- 

 typus is a greatly contorted 

 sac. The wall is furnished 

 with a connective-tissue coat 

 which bears many blood ves- 



FIG. 306. Bit of renal epithelium from the gasteropod 

 mollusk Sycolypus. bl., a blood sinus containing 

 blood cells and coagulated blood; ex., large excretion 

 particle in cell; ex.gr., a second kind of excretion sub- 

 stance in other cells. X 1000. 



sels. These vessels open 

 into sinuses along the base- 

 ment membrane of the 

 nephridial epithelium. Figure 306 shows coagulated blood serum con- 

 taining blood lying next to the basement membrane. One corpuscle 

 bears granules which resemble the excretion granules found in certain 

 of the epithelial cells of the renal sac. 



The epithelium forms no varied regions in the sac. It is composed 

 of tall, columnar cells measuring in height about forty-five or fifty microns. 

 These cells are all ciliated. Oval nuclei lie usually in the basal third of 

 the cell. This is not a constant position for the nuclei. In some cases 

 nuclei may appear quite near the distal ends of the cells. The various 

 nuclei do not stain uniformly in iron haematoxylin. The cytoplasm is 

 alveolar to highly vacuolated. The cells present two conditions. In 

 one condition the cell body is rounded, tending to be cylindrical. The 

 cytoplasm here is greatly vacuolated, and contains one or two rather large 

 excretion bodies or bears no excretion particles. In the other condition 

 the cells become greatly flattened so that they become somewhat fan- 

 shaped. These bear numerous refractive, angular excretion particles 

 (Fig. 306, ex.gr.). 



The nephridial tubule of Lumbricus. This tubule is differentiated, 



