SPINNING MOLLUSCS. 313 



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, 

 Belanger 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 Belanger's 

 statements about the suspensory thread. They appear to have 

 been at considerable pains, however, in attempting, unsuccess- 

 fully, 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 



