A new approach using comparative neuromorphology is taken in this study dealing with the organization of the efferent nuclei of cranial nerves. The authors use the cobalt labelling technique to identify neuron types and follow their presence, or absence, in different animal species. They suggest a new classification which is free from a number of controversies inherent in the classical classification. The results suggest that evolutionary changes in the center and in the innervated periphary parallel each other with increasingly complex function.