414 PROCEEDINGS OF THE ACADEMY OF [July, 



wandered for 110 minutes after leaving the capsule and then reached 

 the surface by a different method. Letting go from its substratum 

 this snail floated up and proceeded to crawl on the surface film, precisely 

 Hke an adult snail. 



3. In this experiment the snails without exception rested at night. 

 The lack of activity may be due to slightly cooler water, yet the dish 

 was kept in a warm room all of the time. Although these snails had no 

 experience of the oustide world, yet they acted, as far as this experiment 

 indicates, exactly as adults. 



Walter ('06) has given us the most complete account of the bionomics 

 of Lymncea. Using his work as a basis it is necessary to call to mind 

 certain activities of the animal. Lymncea has four methods of loco- 

 motion, which may be roughly described as gliding, hunching, dangling 

 and dropping. The last two methods are rare and it is not necessary to 

 consider them in this place. The first method is the most common. 

 It consists in the cilia of the foot beating on a path of mucus secreted by 

 the animal and attached to the substratum. When the snail is oui of 

 water, when its supply of mucus is inadequate and when certain stimuli 

 are applied the snail resorts to the hunching method, which consists of 

 muscular movements of the foot which bring the snail forward. This 

 is something like the movements of a measuring worm. Whatever 

 method the snail uses it is attached to some substratum, whether it be 

 the sides of the aquarium or the surface film of the water, or suspended 

 by a string of mucus from the surface film or anchored by a string of 

 mucus from the bottom. In these ways the snail can browse on 

 water plants, on the sides of the aquarium, and gather the algse floating 

 on the surface (Plankton fishing of Brockmeier, '98) ; but cannot gather 

 any amount of food suspended in the water. 



We have seen by the experiments of Hogg, Semper and De Varigny 

 that certain external conditions will inhibit growth in Lymmea. It is 

 interesting to know just what structural differences exist between the 

 full-grown snail, the dwarf and a normal growing snail the size of the 

 dwarf. Hogg ('54) noticed that the dwarfed snail had many charac- 

 teristics of the newly hatched individual. 



A comparison of the structure of a dwarf with a j'oung snail of equal 

 size that was being raised under favorable conditions, and a comparison 

 of the structure of a dwarf with a snail of the same age that had spent 

 its growing period under favorable conditions and therefore much 

 larger, will show certain relations. These relations are as follows : 



1. Of snails the same size but not the same age the number of whorls 

 of the shell are the same. 



