There is some evidence that in this group the ectoderm of the oesophagus is chiefly concerned with digestion, whereas the endoderm of the intestine is limited to the absorption of the soluble products.
It has been sought to prove that the interior of the hypostome is lined by ectoderm, so as to form a stomodaeum or ectodermal oesophagus similar FIG.
Anteriorly these chords embrace the oesophagus and unite with the cerebral mass which innervates the pair of eyes when present.
In the anthopolyp the blastopore is carried inwards by an in-pushing of the body-wall of the region of the peristome, so that the adult mouth is an opening leading into a short ectodermal oesophagus or stomodaeum, at the bottom of which is the blastopore.
A buccal cavity, a pharynx, an oesophagus and an intestine are always distinguishable.
The oesophagus is provided often with caeca which in Syllids and Hesionidae have been found to contain air, and possibly therefore perform the function of the fish's air-bladder.
Pharynx and oesophagus are concealed in the head.
The oesophagus expands into a curious gizzard, which is armed internally with large horny processes, some broad and thick, others spinous, fitted to act as crushing instruments.
There is no armature, and no glands, and the whole tract can only be divided into an oesophagus and an intestine.
This bilobed sac becomes entirely the liver in the adult; the intestine and stomach are formed from the pedicle of invagination, whilst the pharynx, oesophagus and crop form from the stomodaeal invagination ph.