TAXONOMY AND EMBRYOLOGY - AN ANCIENT AND FRUITFUL CONNECTION

The current system of animal classification relies on the number and s tructure of the germ layers built by early embryos. This system dates back to the beginning of the XXth century. In spite of the increasing influences exerted by phylogenetic studies on taxonomy, there has been no fundamental modification of the development-based system of classi fication. This is not surprising. A certain parallelism exists between development and evolution. When related animals are compared, more si milarities can be detected between their embryonic forms that between their adult ones. Like animals have late diverging developments; unlik e animals have early diverging developments. A similar trend can be di scerned in evolution. Closely related groups have a recent origin; dis tantly related groups have a more ancient origin. Therefore, a develop ment-based taxonomy is likely to reflect phylogeny.