The nervous system of Loligo . V. The vertical lobe complex

Abstract

The vertical lobe system is described in Loligo and Sepia . It receives inputs from the optic lobes, arms, mouth and skin receptors. These inputs are combined and passed through a system with several superimposed loops. The output includes large neurons reaching to control centres for the arms and mantle, which initiate movements of attack or retreat. Another part of the output passes back to the optic lobes. The vertical lobe system receives no input from the statocyst and has few connections with the basal lobes. The inferior frontal lobe allows interaction of impulses from the arms, mouth, mantle and skin. Its outputs pass to the buccal mass and arms and upwards to the superior frontal lobe. The latter has two parts comparable to those found in octopods, communicating with the vertical and subvertical lobes. The inferior and superior frontal lobes contain no microneurons with axons restricted to the lobe. The vertical lobes are strikingly different from those of octopods. They are not divided into lobules, they have many large cells and an extensive neuropil. Numerous microneurons, with axons not leaving the lobe, arise in the peripheral parts of the vertical lobe. The organization of the neuropil differs in the six lobes that make up the system. In the inferior frontal lobe all the inputs can influence any of the cells. In the superior frontal lobe the neuropil is layered and the topology of the optic lobes is probably preserved. In the vertical lobe large neurons are scattered throughout the neuropil among the processes of the microneurons. The subvertical and precommissural lobe neuropils allow many influences to converge on large output cells, which are also accompanied by microneurons.