424 PEOCEEDINGS OF THE ACADEMY OF [July, 



Another point of importance in these experiments was the fact that 

 in no cases was the water plant attacked when sediment was not 

 present. On the other hand, in jars with sediment present the normal 

 thing was to have the leaves of the water plant cut to pieces. 



To determine whether the presence or absence of sediment would 

 affect the growth processes of the snail a number of experiments were 

 undertaken. The sediment used in Experiments 85, 86, 87 and 88, 

 was mud from the pond in the Botanic Gardens. This was washed 

 and that which settled in from 1 to 5 minutes kept for experimental 

 purposes. Because this mud would probably introduce food into the 

 jars, soil from the garden bed was taken, boiled and that which settled 

 in from 1 to 5 minutes used in Experiments 89 and 90. In Experi- 

 ments 118-121 the sediment was boiled in concentrated nitric acid, 

 evaporated to dryness, and ignited. This would surely destroy all 

 organic matter; yet the results of these experiments continued to show 

 the benefit of the sediment. Quartz sand and quartz pebbles washed 

 with nitric acid gave beneficial results also. If the Myriophyllum was 

 washed in running water the snails did not grow as large as if it was 

 used with the particles of sediment still clinging to the leaves. 



In conclusion it seems probable that (1) the muscular gizzard filled 

 with sand is necessary to break up the plant cells that have been torn 

 off by the radula. (2) The absence of sand seems to have the effect 

 of causing the snails not to rasp off cells from the tissues of water plant. 

 (3) If there is enough small algae present, Myriophyllum will have Httle 

 or no effect on the growth. (4) An examination of the stomach of 

 small snails under 5 mm. shows that such plant tissue as Myriophyllum 

 is not eaten. With snails 5 to 12 mm., however, great gashes are torn in 

 the leaves, and the stomach is filled with the crushed cells. (5) The 

 discordant results of Tables I and II are no doubt due to the presence 

 or absence of sediment. 



Fceces. — The amount of fseces produced by Lymruea is enormous and 

 Walter ('06) reports that Lymncea elodes forms cylinders of fsecal mat- 

 ter fourteen times its own length every twenty-four hours. This 

 collects at the bottom of the aquaria in great tangled masses. 



De Varigny ('94) investigated the effect of this material on the 

 growing snail. The result of his experiments was the stunting of the 

 snails in the jar with the fsecal masses. In repeating these experi- 

 ments of De Varigny the writer gathered fseces from a jar in which a 

 snail had been living for a month or two. This matter in some cases 

 was washed in a filter and in others by decanting. This washed 

 material was added to jars of snails. The result indicated in Table IV 



