It is further noticeable that in Rhynchelmis the covering of vesicular cells which clothes the drainpipe cells of the adult nephridium is cut off from the nephridial cells themselves and is not a peritoneal layer surrounding the nephridium.
The tail may be a simple hollow muscular process or provided with stiff bristles set in transverse rows, or divided into two equally long processes, or finally it may form a large vesicular structure.
When the true skin is inflamed various appearances may arise, according to the intensity and extent of the inflammation, and the eruption may be papular, vesicular, pustular, tubercular, bulbous or ulcerative.
The thicker portion develops a terminal muscular rostellum and two or four suckers, the thinner end (" tail ") is vesicular, more or less elongated, and contains the six embryonic hooks.
Minute vesicular cavities are not infrequently present, sometimes as negative cubes, and these may contain saline solutions or carbon dioxide or gaseous hydrocarbons.