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Besides the seals and cetaceans, the sea cows (Sirenia) may be said to represent the most marked adaptation to aquatic life of all mammals.A distinguishing feature of the sea cows is that they are the only forms of herbivorous mammals which are adapted exclusively to aquatic life. Compared with the great number and variety of seals and cetaceans the sca cows form a strikingly small order, comprising only the marine dugongs with three closely interrelated geographical races (Halicore dugong, Halicore hemprichi and Halicore australe) inhabiting the coastal waters from East Africa and India to Australia, and the three species of manatee living in fresh or brackish water, Trichechus latirostris from Florida to northern Brazil, Trichechus inunguis in Brazil and Trichechus senegalensis in West Africa (Weber, '28). It was considered to be of interest to try to outline experimentally the respiratory characteristics of a sea cow, especially with a view to its adaptation to prolonged diving, and to relate the analytical data from the sea cow especially to those obtained from seals Previous w7ork on the respiration of sea cows is confined to observations of their breathing rate and diving times in captivity. Particularly valuable are the systematic observations by Parker ('22) on three Florida manatees (Trichechua latirostris), the same species as our animals. The size of his animals were: I, less than 2 m, 11, 24 m, and 111, 3 m. The average diving times were respectively 43 minutes, 8+ minutes, and 12 minutes. The average number of breaths taken per 10 minutes was 3.1, 2.4 and 2.2. The loiigest diving time was observed in the biggest animal with a maximum of 16 minutes and 20 seconds. Parker's observations, redrawn after his