Fig. 2. Basic structure of the mammalian (A) and arthropodian (B)
central nervous systems. At the right of each system are indicated its
traditional subdivisions. The common (ancestral) structure is deduced in
(C). The vertical hatching identifies the midbrain-hindbrain boundary in
vertebrates and the homologous structure in insects. The light gray
identifies the cephalized regions of the nerve cord: hindbrain in vertebrates,
tritocerebrum and suboesophageal ganglion in Drosophila. Abbreviations:
F, forebrain; M, midbrain; H, hindbrain; *, oesophagus.