The species concept is one of the oldest and most fundamental in biology. And yet it is almost universally conceded that no satisfactory definition of what constitutes a species has ever been proposed. The present article is devoted to an attempt to review the status of the problem from a methodological point of view. Since the species is one of the many taxonomic categories, the question of the nature of these categories in general needs to be entered into.

Présentation d'un manuscrit du IXe siècle, le Codex Athous, Panteleemon 288, qui contient une collection de 34 homélies ainsi que l'oraison funèbre de l'empereur Léon VI . Au début du manuscrit, on trouve un court poème faisant l'éloge de Léon VI en tant qu'homiliste.