Hence both polyp and medusa present characters for classification, and a given species, genus or other taxonomic category may be defined by polyp-characters or medusa-characters or by both combined.
The former is concerned with the division of the earths surface into major districts characterized by particular plants or taxonomic groups of plants, with the subdivision of these floristic districts, and with the geographical distribution (both past and present) of the various taxonomic units, such as species, genera, and families.
The taxonomic importance of the configurations of the palate was first pointed out by J.
Between them arises a median crest, which varies much in extent and composition, and is of considerable taxonomic value.
The extent of the origin of this muscle from the sternum, on which it leaves converging, parallel or diverging impressions, is of some taxonomic value.