NEPHRIDIAL TISSUES 



351 



mirabile; i.e. it forms a capillary network connecting two vascular struc- 

 tures of the same character. The branching capillaries, before they leave 

 the glomus, are reunited and the efferent vessel is formed, which is also 

 an arteriole but slightly smaller than the afferent arteriole. The capillary 

 plexus is supported by a slight framework of connective-tissue cells 

 (Fig. 313). The glomus of Iguana measures about fifty microns in 

 diameter. Figure 313 shows a section of a glomus from the kidney of 

 this animal. The capillaries cut at various angles and filled with blood 

 corpuscles appear in this section as dense bodies with a well-defined out- 

 line. Closely applied to this contour at places the flat nuclei of the cells 

 of the capillary wall are seen in transverse section (Fig. 313, c.n.\ 

 These, except for their position, resemble much the nuclei of the termi- 

 nal epithelium of the tubule. The nuclei of the connective -tissue cells 

 are as a rule smaller than those of the cells of the capillary wall, and 

 of the terminal epithelial cells (Fig. 313, conn.t.). 



The terminal epithelium is composed of thin, flat, polyhedral cells 

 which are continuous with the main portion of the tubule. After the 

 tubule leaves the glomus its wall presents two types of cells histologically 

 quite different. The tubule near the capsule is convoluted. This con- 

 voluted region is the larger of the two. Its diameter may be thirty-five 

 to forty microns. The cells are stout columnar forms. In transverse 

 section they appear as sections of truncated cones or pyramids. They 

 measure twelve to fifteen microns in height. The inner margin of 

 the cytoplasm has an irregular contour and tends to be striated. Be- 

 neath this there is a zone of finely granular cytoplasm which bears ex- 

 cretion particles. This zone occupies the greater part of the distal end 

 of the cell. The 

 basal or proximal 

 part of the cyto- 

 plasm is more or 

 less definitely stri- 

 ated and may con- 

 tain vacuoles. The 

 striae are by no 

 means as conspicu- 

 ous as those shown 

 in the nephridial 

 cells of a frog (see 

 Fig. 174). The nu- 

 clei are rounded 

 and contain a dis- 

 tinct reticular network with small, rounded chromatin bodies, and one 

 large chromatin mass which may inclose a nucleolus (Fig. 314). 



FIG. 314. Sections of a thick and a thin region of the nephridial 

 tubule of an Iguana. X 870. 



