The arrangement of the myenteric nerve-plexus is simpler in fish, much simpler in Amphioxus, than in the higher forms. The nerve-cells in it are not grouped into distinct ganglia at the points of crossing of the fibre-bundles. In Scylliorhinus only two or three cells are present at such points, while in Teleosts the nerve-cells are situated in the meshes of the plexus, as is also the condition in Amphioxus.
In Scylliorhinus these nerve-cells are all of Dogiel's type II; in Teleosts they belong to both types I and II. In Amphioxus bipolar nerve-cells are definitely present in addition to the stellate ganglion cells described by Boeke.
Synapses between (a) the pre-ganglionic fibres and the enteric neurons, and (b) the enteric neurons themselves are figured and described.
The ‘interstitial cells’ of Cajal are present in the muscle-wall of the gut of fish. A connexion between this system and the enteric plexuses is not to be observed.
The enteric plexuses of fish and Amphioxus are not in the form of a nerve-net. It is not possible to compare the enteric plexus of Amphioxus with the system of ‘interstitial cells’ of the higher chordates. The stellate ganglion cells of Amphioxus are to be compared with the neurons of type I in the higher forms.