1. The respiratory and cardiac responses to stopping and starting the water supply to the gills, to increasing and decreasing the rate of flow, and to complete interruption of the blood supply to the medulla of Scyllium canicula were recorded. 2. Sudden stopping and starting or increasing and decreasing the water supply evoked brief respiratory inhibition and sometimes ejection reflexes. 3. An increase in the rate of flow of sea water to the gills caused an increase in respiration and heart rates. A decrease caused the reverse. Too great an increase, however, evoked irregular inhibition. 4. Stopping the flow of water to the gills evoked brief inhibition of respiration followed by a regular rhythm at first, which sometimes became periodic and finally was interrupted by generalized muscular activity. The medullary centers remained reflexly functional for over three and one-half hours. 5. Interruption of the blood supply to the medulla when there was no water supply to the gills was followed by regular respiration at first, then periodicity and dyspnea. The medullary centers remained reflexly functional for over sixty minutes without a blood supply. 6. It is concluded that the respiratory center is autonomous, but that it is influenced by the gas content of the blood and by peripheral stimulation.