A GOOD EYE FOR ARTHROPOD EVOLUTION

Insect and crustacean lineages diverged over 500 Myr ago, and there ar e continuing uncertainties about whether they evolved from a common ar thropod ancestor or, alternatively, they evolved independently from an nelid worms. Despite the diversity of their limbs and lifestyles, the nervous systems of insects and crustaceans share many common features both in development and in function. Cellular and molecular embryology techniques reveal good evidence for homologies in the developing segm ental ganglia. In the visual system, this seemingly common programme o f insect and crustacean CNS development culminates in common adult neu ral function. Comparisons of the cellular anatomy and physiology of an imals as diverse as flies and crayfishes indicate that the neural circ uits in the lamina of their optic lobe have been inherited largely unc hanged from a common ancestor with good compound eyes.