BIOLOGY OF PHYSA 67 



surface of the water. My observations in field and laboratory- 

 failed to confimi this statement. In the field, one finds the 

 snails most of their time on the bottom or among weeds, accord- 

 ing to the kind of habitat. In the laboratory, they reach the 

 surface of the water often but do not stay crawling on the sur- 

 face of the water for long at a time. The reason is obvious if 

 one watches a snail on the film, especially in a small aquarium. 

 When the animal comes within a cm. or so of the side of the 

 dish or other like solid, it seems, at least to the uninitiated, to 

 hasten its speed and crawls under the water as though relieved 

 to get upon a solid. In reality, however, the reason the snail's 

 speed is thus increased when it comes within a certain distance 

 of the glass sides of the aquarium is due to the approximation 

 of two bodies that will not wet, the glass and the snail. The 

 snail's head is brought up against the glass with some force 

 which causes it to lift the head away from the film and to crawl 

 at once down the side of the glass into the water. This is an 

 almost invariable result if the snail is approaching the side of 

 the dish head first. It often happens that the snail comes up 

 to the side of the dish and eats with its foot partly on the glass 

 and partly on the film. The action of the surface film causes 

 the snail, however, to be brought back against the side of the 

 dish, usually with force enough to cause it to crawi down in 

 the water. It is thus seen that, w^hile a snail comes up to the 

 film quite frequently in a small aquarium, its stay there is lim- 

 ited. Tye speaks of some species of snails spinning when young 

 but ceasing to do so when they grow to be adults. I have made 

 no observations which substantiate this view-. Lymnaea stagnalis 

 has never been seen to spin although it has been reared from 

 the egg in the laboratory. 



Walter (1906) has the following to say upon spinning: " Occa- 

 sionally a snail will be seen dangling in the middle of an aquarium 

 without any visible means of support, but by passing a brush 

 gently through the water a mucous thread will be discovered 

 anchoring the snail, usually to some object at the bottom of 

 the aquarium. A snail thus attached to the bottom by a mucous 

 thread may be seen to gradually spin its way to the surface, the 

 foot meanwhile being rolled into a tube instead of spread out flat. 

 Again, a snail, made light by air bubbles, will sometimes climb 

 down such an anchorage, in which case a stroke of the brush 



