and when the branch was left floating at the surface some ascended to it by the thread, while others fell again to the bottom. Another observation, which the author regarded as of much interest, was as follows:—He saw issue from two or three of those which were at the bottom of the bucket a little bubble of air, which rose slowly; and, in trying to move it with a frond of the weed, he saw the animal—holding to the bubble by means of its silk—rise through the water. Speculating upon this last observation, Bélanger supposes that the creature would not be entirely lost even if the shaking, which had detached it from the weed, were also strong enough to break its thread; though not anchored it would still have a lifebuoy, and this buoy, floating on the surface of the water, and coming in contact with another plant, would enable the animal to ascend to a new home. Further, the author even thought it possible that the creatures might thus voluntarily change their positions; a family, he supposes, might find their plant insufficient to feed their increasing numbers; whereupon some of them, seeking new feeding-grounds, might abandon themselves to the water, and wait, suspended to their bubbles, till a new plant chanced to be carried to them by the waves. Finally, on Aug. 27th, the creature still occurred on the weed, but in small quantity, and mostly very young. Of those which remained suspended after the weed had been shaken, one of the larger ones was observed, while thus hanging in the air, to reascend by its thread. Placing the animals at the bottom of a bucket of water, the observer left them for the night; but in the morning all were dead, none having ascended to the surface or to the floating weed. Eydoux and Souleyet obtained numerous specimens, and, on shaking the weed on which the animals were brought up, they had no difficulty in confirming Bélanger's statements about the suspensory thread. They appear to have been at considerable pains, however, in attempting, unsuccessfully, to confirm the observations about the mucus-invested air-bubble; specimens were placed at the bottom of deep vessels of water, and allowed to remain there for a considerable time, but none ascended by means of a bubble. Some crept up the sides of the vessels to the water-surface, under which they crept like other gastropods. The appendages which characterize the upper part of the foot of Litiopa may be useful, these authors think, in
