A new approach using comparative neuromorphology is taken inthis study dealing with the organization of the efferentnuclei of cranial nerves. The authors use the cobaltlabelling technique to identify neuron types and followtheir presence, or absence, in different animal species.They suggest a new classification which is free from anumber of controversies inherent in the classicalclassification. The results suggest that evolutionarychanges in the center and in the innervated peripharyparallel each other with increasingly complex function.