434 PROCEEDINGS OF THE ACADEMY OF [July, 



Effect of Shell Salts. — If it were possible to measure some other 

 physiological process of the snail than growth, another method might 

 be instituted to attack the study of the effect of environment. As it 

 is possible to measure the activity of a certain tissue in the pond snail 

 by the amount of its secretions, a series of experiments were con- 

 ducted. The tissue referred to is the mantle which secretes the shell. 

 With this in mind a few experiments with calcium carbonate, calcium 

 sulphate, and calcium phosphate. Snails that had been raised in 

 saturated solutions of these salts, which are but shghtly soluble in 

 water, were measured; the results are expressed in Table XII. The 

 salts were supphed as the pure chemical or as ground-up Lymncea shell. 

 The results show that calcium sulphate is most beneficial and that the 

 presence of shell salts are favorable to snail growth. Experiments 

 55-56 did not consider that the sediment of the ground mineral might 

 introduce another factor. Experiments 201-204 consider this factor. 

 The fact that each chemical seems to favor a separate flora introduces 

 another factor which makes these experiments most unsatisfactory. 



Number of Individuals. — Semper ('74) and De Varigny ('94) both 

 reported that in two similar jars, one containing one snail and one 

 containing many, the single one grew the larger in every case. This 

 fact was one of Semper's strongest arguments in favor of the presence 

 of an unknown chemical. De Varigny could not explain this result 

 on his exercise theory, so he advanced a psychological theory based on 

 the fact that two snails might annoy each other. He writes: "Mais 

 que pent etre cette influence morale dans le monde des Lymnees? Le 

 probleme est embarrassant, et je n'ose decide si la presence de deux 

 L3rmnees gene ou ne gene pas le peregrinations de la troisieme, etc." 

 (p. 187). 



The result of the experiments reported in Table VI of the present 

 work confirm the results of the authors who have investigated this 

 factor. Discarding both Semper's and De Varigny's explanation, we 

 must turn to a consideration of those of the later authors. Willem 

 ('96) explained the result as due to aeration, but it seems rather that 

 Vernon's ('03) explanation is more nearly true. Vernon considers 

 that the toxic influence of accumulations of the waste products of 

 metabolism is the cause of the dwarfing, yet increased aeration will 

 insure more rapid oxidation of those waste products and so remove 

 their harmf ulness. 



From what has been said it will be seen that the chemical composi- 

 tion of the water is a very important factor in the rate of growth of 

 Lymncea. The composition of the water may exert a toxic or a bene- 



