Insects and Vertebrates: Analogous Structures in Higher Integrative Centers of the Brain

This work deals with studies on anatomical relationships, neuronal composition, and some synaptic connections that exist in the central complex (CC) in the supraesophageal ganglion in larva of dragonfly g. Aeschna. It has been shown that CC contains protocerebral bridge of an elongated and slightly curved cylindrical shape, fan-shaped and ellipsoid bodies of a bean-like shape and two small roundish noduli. There were revealed (stained) neurons providing both internal connections of CC and its connections with other CNS regions. Connections with tritocerebrum, the higher center of the autonomic nervous system, and subesophageal ganglion, an intermediate relay between supraesophageal ganglion and truncal brain, have been established. The existence of connections of CC with nuclei of abdominal nervous chain is suggested. Connection of ocelli with the CC has been traced. Unipolar neurons of the same type have been revealed, each of them giving collaterals to protocerebral bridge and ending as bushy terminals that form the main part of glomerule in the fan-shaped and ellipsoid bodies. Glomeruli are arranged in rows, in which cross connections have been found. It has been established that the structure of neuropils of the fan-shaped and ellipsoid bodies represent a shielding structure described in the cerebral cortex, midbrain cortex, and cerebellar cortex of vertebrates. Thus, in insects, like in vertebrates, the shielding structures developed not only in optic centers, but also in structures performing higher integrative functions. A possible functional role of the central complex is discussed.