which a number of thread-like filaments protruded from the lower part of the head are engaged from time to time in feeling, and apparently examining. When this hollow is sufficiently wide and deep, the animal tilts its tube into it, by protruding until the weight of its body overbalances the supported part; it proceeds with its excavation, the tube becoming more and more inclined, until at length it is brought to the perpendicular, when it descends straight down till it is completely buried, the sand closing over its disappearing extremity.
This burrowing habit, the mouth of the tube being downward, makes it needful that there should be a posterior orifice in the tube. All the tribe to which this species belongs are nourished by those minute organic atoms which are held in suspension by the water, and which are brought by strong ciliary currents to the mouth. The currents thus produced are subservient to the two functions of respiration and digestion, the water thus hurled along giving off its Oxygen to the gills, and its organic atoms to the stomach. The refuse water, kept in unflagging motion by vigorous cilia, is poured from the terminal extremity of the body, and discharged through the minute orifice that I have described.
Dr. Williams, in his admirable 'Report on the British Annelida,' has, I think fallen into an error with regard to this species; or at least his statements in this particular do not agree with my own observation. After describing the mode in which the posterior extremity in A. alveolata is contracted into a true cylindrical tail, which, turning upwards, returns along
