The substance will then diffuse from the posterior segment into the anterior one, giving concentrations as shown in Figure 14c.
The posterior segment is flattened and bears no chaetae.
The head and the posterior abdominal segments are relatively small and dark-coloured.
The posterior segment may be fused with anterior part of a simple and small pygidium.
Rarely, it may extend to the posterior segment to cause endophthalmitis in later stages, leading to the destruction of the eye.
In some species the two posterior abdominal segments are reduced.
The air pressure is temporary as the posterior segment will soon re-fill with fluid.
When mature, a number of its posterior segments gradually develop into one or more sexual individuals which finally break away and swim free in the sea.
The posterior segments of the worm bear hooked bristles which help anchor it in its tube.
Abdomen: The posterior abdominal segments are extensively modified for reproduction.