ABSTRACT
Dipnoan lungfish have evoked considerable interest over the last two centuries. These fish belong to a subclass of osteichthyes which flourished during the early Paleozoic era. This subclass comprises only three surviving genera: Neoceratodus, Protopterus and Lepidosiren. Lungfish represent an old step endowed with the full panoply of an air-breathing vertebrate. Some elements of this panoply are still present in newborn humans. Due to lack of information concerning the vasculature of fossilized species, there is no witness to the evolutionary steps that led to its organization in extant lungfish. Vascular casts show that the location of the ductus is quite similar in Protopterus aethiopicus and in Lepidosiren paradoxa. In contrast to Neoceratodus, a facultative air-breather relying mainly on gills for respiratory gas exchanges, Protopterus and Lepidosiren are obligatory air-breathers. The relationship between phylogeny and ontogeny has been a matter of debate for more than a century. According to a very popular concept individual development repeats the history of the race.
