The late zoologist Sidnie Manton acknowledged that arthropods- animals with jointed exoskeletons, such as flies, crabs, and spiders- are all descended from soft-bodied segmented worms. Yet he maintained that differences in limb form, musculature, and embryonic development indicate that these three arthropod groups- insects, crustaceans, and chelicerates, respectively- evolved independently from worms rather than from a common arthropod ancestor. Consequently, according to Manton, shared characteristics such as a jointed exoskeleton and large compound eyes represent cases of convergent evolution- similar yet independent developments- in these organisms. But if they evolved convergently, then one would expect significant differences in the neurological systems supporting sight. In fact, however, many nerve cells play virtually identical roles in supporting complex visual responses in both insects and crustaceans, suggesting that their common ancestor already possessed highly developed eyes, and therefore was probably already an arthropod. Yet the compound eyes of chelicerates differ neurologically from those of insects and crustaceans, suggesting that the eyes of chelicerates did evolve independently and providing partial confirmation of Manton's views.