190S.] NATURAL SCIENCES OF PHILADELPHIA. 447 



a jar affect the rate of growth. The cause is probably due to increased 

 secretions and perhaps to diminished aeration. 



7. Calcium salts in the water seem on the whole beneficial to growth 

 — calcium sulphate particularly so. 



8. Growth of Lymncea is inhibited by cold, as Semper reported. This 

 factor may act in two ways — directly on the physiological processes of 

 the animal and indirectlj^ through the inability to procure food, the 

 snail becoming too sluggish to search for it. 



9. Area. The cause that De Varigny advanced to explain dwarfing 

 was lack of exercise on the part of the snail. The greater the place to 

 crawl, the greater the snail. However, when aeration was kept con- 

 stant, which De Varigny failed to do, the results were not significant. 



10. Volume. That the volume of the medium affects the growth of 

 Lymncea is certain. Willem explains the fact on the ground of aeration. 

 The author accepts this view, but considers that the more concentrated 

 excretions in smaller volumes must play an equal part. 



11. Alternate Conditions. Snails under unfavorable conditions 

 when placed under favorable ones grow faster than if they were con- 

 tinuously in favorable conditions. It would seem that the change 

 from unfavorable to favorable conditions of life acts as a stimulant for 

 growth. However, this does not always mean that it surpasses the 

 control size. It rarely does that. 



12. Not only does the environment affect growth, but it affects the 

 number of eggs laid in a given time. This fact is very important, 

 because it shows that the environment probably affects all the physio- 

 logical processes and not one alone. 



13. This study reveals the fact that confinement influences the 

 growth of aquatic animals in three ways — through the amount of food, 

 through the amount of oxygen and through the accumulations of the 

 waste products of metabolism. The phenomenon is not a simple one 

 and each factor plays its own part. 



Literature Referred to, 



Bessey, C. E. 1892. Botany, 7th edition. 



BROCKMEiEii, H. 1898. Siisswasserschnecken als Planktonfischer. Forch-Bci . 

 Biol. Sta. Plon., Th. VI, p. 165. 



Clowes, F., and Coleman, J. B. 1903. Quantitative Chemical Analysis, p. 323. 



Cooke, A. H. 1895. Cambridge Natural History, Mollusks, pp. 94-95. 



CuviER. 1817. Memoire SUV le Limnee et le Planorbe. 



Dandino, J. B. 1904. Relation of Mass Action and Physical Affinity to 

 Toxicity, with Incidental Discussions as to how far Electrolytic Dissociation 

 may be Involyed. Am. Jour. Sci., ^^ol. XVII, 4th series, p. 437. 



Davenport, C. B. 1899. Experimental Morphology, ^'ol. II, pp. 473-478. 



