The skull is abnormally thick and the cerebral capacity small.
G 2, Cerebral ganglia.
The eyes are indicated as black dots behind the cerebral ganglia.
The figure B also shows the peculiar neural investiture formed by the cerebral arteries in Limulus and the derivation from this of the arteries to the limbs, III, IV, VI, whereas in Scorpio the latter have a separate origin from the anterior aorta.
In some Lamellibranchs the osphradial ganglia receive nerve-fibres, not from the visceral ganglia, but from the cerebral ganglia along the visceral commissure.