En el capítulo II de su libro Essay on Classification, Agassiz pone todo su empeño en describir lo que son las categorías taxonómicas. Empieza así el capítulo:   The use of the terms types, classes, orders, families, genera, and species in the systems of Zoology and Botany is so universal, that it would be natural to suppose that their meaning and extent are well determined and generally understood; but this is so far from being the cause that it…