Black droplets of oil are seen in the epithelial cells lining the secreting tubules.
Belonging primarily to the epithelial layer, the muscular cells may become secondarily sub-epithelial.
of this are formed of epithelial cells, bounded towards the lumen of the pit by a very delicate cuticular membrane continuous with the cuticle covering the surface of the body.
The epithelial layer consists of (1) so-called " indifferent " cells secreting the perisarc or cuticle and modified to form glandular cells in places; for example, the adhesive cells in the foot.
Over the latter the dense white smooth epithelial lining of the oesophagus is continued, terminating abruptly by a raised crenulated border.