Comparison of neurotransmitter cell types in amphioxus embryos with the distribution of ventrolateral neurons in amphioxus larvae. A: Neurochemical map of amphioxus 20–24 hr embryos. B: Distribution of ventrolateral neurons in amphioxus 8–12.5 day larvae. Anterior is up and neuronal distribution is indicated only until the level of somite 3. Boundaries between somites (S) are used to indicate the relative position of different cell types in the neural tube. Motoneuron populations include dorsal compartment motoneurons (DC), ventral compartment motoneurons (VC) and visceral motoneurons (VM). Interneuron populations include the large paired neurons (LPN) and the ipsilateral projection neurons (IPN).