The relation between the power and extent of migration in certain species, either at the present or at some former period, and the existence at remote points of the world of closely allied species, is shown in another and more general way.
Espezie batzuek oraingo garai honetan edo lehenagokoren batean izan duten emigrazio ahalmen edo hedaduraren eta munduko puntu urrunetan espezie oso hurbilak existitzearen artean dagoen erlazio hori beste modu orokorrago batez ere azaltzen zaigu.