Pulmonata 521 



tions. The closest kind of inbreeding has been practiced, each young 

 snail being isolated in a jar by itself, and a race has been established of 

 a gametic purity rarely attained in animals. Nevertheless, the race 

 shows remarkable hardiness and longevity. 



Since Lymnaea columella reacts readily to slight environmental 

 changes, a controlled environment becomes necessary. The standard 

 medium for a single snail is 500 cc. of filtered pond water placed in a 

 4 1 //' x 5" battery jar. The jar containing the snail is kept at room 

 temperature which, between October and April, ranges from iq° to 

 22 C. with a mean of about 21 . In the summer months a temperature 

 approaching 30 accelerates development. 



Chemical analyses of the medium show that the water in which the 

 snail lives is practically without oxygen. Since the snail is air-breathing, 

 this anaerobic condition offers but slight disadvantage to the animal 

 (Colton, 1908; Walter, 1906). 



For food, dried leaves of the Carolina poplar are introduced, one at a 

 time. Small tender leaves are chosen at first, when the snails are small, 

 and larger, tough leaves later. It is necessary to add but few leaves 

 at a time and to add no leaves that appear green, for these seem to form 

 a favorable medium for bacterial growth. The bacterial scum from 

 such leaves keeps the young snails from reaching the surface and causes 

 them to drown. Dried leaves may be gathered in the autumn and kept 

 indefinitely. 



As the senior author pointed out some years ago (Colton, 1908), 

 this snail has a true gizzard containing small stones. These small stones 

 are necessary for the breaking up of plant tissue. Without stones the 

 animal starves amfd abundance. Therefore, it is necessary to introduce 

 a pinch of soil into each jar. 



Even under standard conditions there is considerable variation in the 

 time between the laying and the hatching of the eggs. If sexual ma- 

 turity is considered as the time of laying the first eggs the time of reach- 

 ing this stage is also variable. In general, when a snail reaches the 

 length of 10 mm. it usually lays eggs, but the range extends from 7 mm. 

 to 12 mm. The first eggs are usually laid forty days after hatching. 

 This interval is much longer in the autumn, often extending over three 

 months, and is shortest in the spring, when it may be only five weeks. 

 The factor prolonging the life cycle in the autumn is neither food nor 

 temperature and at the present time is unknown and uncontrolled. 



M. E. D. 

 Bibliography 



Colton, Harold S. 1908. Some effects of environment on the growth of Lymnaea 



columella Say. Proc. Acad. Nat. Sci. Phila. July, p. 410. 

 1 91 2. Lymnaea columella and self-fertilization. Ibid. May, p. 173. 



