Messenger, J. B.; (1965) The peduncle lobe and associated structures in cephalopods. Doctoral thesis (Ph.D), University of London.

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Abstract

1. The peduncle complex, examined in thirteen genera of cephalopods, comprises a non-nervous optic gland and two nervous parts, the peduncle lobe and the olfactory lobe, whose neuropils are continuous. / 2. The complex is closely associated with the optic lobe, from which it derives its main afferent input. There are efferents to motor centres in the central brain and there is a peduncle commissure. The anatomy and function of the complex and its connexions were examined in detail in Octopus vulgaris Lamarck. / 3. The olfactory lobe represents a lateral extension of the dorsal basal lobes it receives the olfactory nerve but its function has not been established, and it is doubtful whether the "olfactory organ" is a chemoreceptor. / 4. The peduncle lobe is remarkable for the orientation of the axons of the cells in one region. In octopods and in Sepia these form a parallel array in the horizontal plane; in other decapods the axons lie parallel but in the vertical plane. It is suggested that this is related to habit and eye structure: both Sepia and Octopus are bottom-living forms and possess a horizontal pupil and retinal strip. / 5. In Octopus, removal of the complexes bilaterally does not abolish the ability to make simple visual discriminations, and does not abolish gross eye movements, which are described for the first time. / 6. Removal of the peduncle complexes bilaterally affects but does not abolish locomotion, which becomes less coordinated and "unstable". Electrical stimulation of the complex produces patterns of motor activity including colour and locomotor responses. / 7. Bilateral removal of the complexes has, however, no effect upon the locomotion of blind octopuses: evidently the peduncle complex (probably the peduncle lobe alone) controls motor activity on the basis of things seen. / 8. The peduncle lobes exert a 'crossed excitation effect' in the absence of the optic lobes, the right peduncle lobe, for example, initiating forward walking movements of the left arms. / 9. This system in the intact animal forms part of a device that ensures motor co-ordination between the two sides of the body on receipt of visual "commands", for Octopus has two eyes and partially monocular vision. / 10. No satisfactory interpretation of the neuropil is established though possibilities are discussed: it is suggested that an electrophysiological Investigation is necessary to resolve this.

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