430 PROCEEDINGS OF THE ACADEMY OF [July, 



In consideration of the above the writer believes the follo\\ing 

 statement of Willem not altogether supported by the facts. Willem 

 ('96) writes, p. 567: "Ces experiences, . . . ., prouvent que chez les 

 Basommatophores la respiration cutanee est plus importante que la 

 respiration pulmonaire et qu'a elle seule, elle pent suffire a la vie de 

 ces animaux." 



3. The Composition of the Water. — The present study considers those 

 conditions alone in which the composition of the water might affect 

 the growth of pond snails under natural conditions. 



Effect of Accumulation of Excreted Matter. — De Varigny ('94) grew 

 snails in water in which a snail had been living for months, with the 

 result that the snails were dwarfed. Vernon ('95) performed similar 

 experiments with Echinoderm larvae with the same result. The writer 

 has conducted experiments of this sort on Lymncea. Table IX expresses 

 the results of eight experiments. These results are as follows: (1) 

 That weak solutions of the waste products of metabolism are of benefit 

 to the snail. (2) That concentrated solutions are harmful. (3) In 

 Experiments 136 and 199 the water was aerated so the factor of the 

 aeration of the water would be constant. In Experiment 143 the 

 water was boiled, yet in these two cases the results were similar. Later 

 the experiments of Table X were repeated with different dilutions of 

 urea with similar results. As these were similar to those found by 

 Vernon ('95), who used also uric acid on Echinoderm larvae, it was not 

 thought necessary to continue the experiments further. 



Analyses of the water. A year before Vernon's ('99) paper was 

 called to the attention of the writer, a series of analyses were made 

 of the water in a number of jars. Although not nearly so extensive 

 as those of Vernon, yet the results were nearly parallel. 



By the methods of water analysis (Clowes and Coleman, '03), the 

 water in the jars of several experiments was analyzed for chlorides, 

 nitrates and particularly for free and for albuminoid ammonia. The 

 free ammonia consists largely of the inorganic salts of ammonia. 

 Albuminoid ammonia on the other hand is made up of organic com- 

 pounds from which the ammonia radicle is not detached by boiling 

 with sodium carbonate. 



Experiments 200 and 201, Table VIII, were conducted in the follow- 

 ing manner: Six jars with 500 cc. of water, which was analyzed 

 before the experiment, were taken. Two were used without water 

 plant or snail as control. The other jars contained snails and water 

 plant as follows: one without water plant but with one full-grown 

 snail, one without water plant but with five snails, one with water 



