CETACEA (from the Greek word κψ-oς, a whale) is the name employed by zoologists to characterize the important order of Mammals which contains the whales and dolphins. These mammals are aquatic in their habits, and possess a fish-like form. They differ from fishes in breathing by lungs and not by gills, in being viviparous and not oviparous, and in suckling their young with a pair of mük-secreting glands or mammae. This order was formerly divided· into two groups the herbivorous cetacea and the carnivorous cetacea. By modern zoologists the herbivorous cetacea, which include the animals called dugong, manatee, and rytina, are not regarded as whales, but are referred to a distinct order named Sirenia. The order Cetacea, therefore, in its present acceptation is limited to the toothed whales or Odontoceti and the whalebone whales or Mystacoceti. For the organization, classification, and distribution of these animals, see Mammalia.