LYMNEIDZ OF NORTH AMERICA. 43 
“Lymneus elodes (palustris) feeds readily on dead flies, tadpoles 
and its own eggs, as well as on other snails when their shells have 
been crushed. It was also seen to engulf and retain the feeces of other 
snails. Brockmeier’s observations of ‘plankton fishing’ in the case of 
Limneus peregra were confirmed. ‘Plankton fishing’ may be described 
as follows: While the snail is floating attached to the surface film 
of the water it will sometimes depress its head-end a little below the 
water’s surface, form a scoop out of the foot, and by means of this 
collect the microscopic organisms and other floating material at the 
posterior end, in a trap formed by the mucus which continues to flow 
out backward, even after the animal itself has become stationary. As 
soon as sufficient food has been collected, the snail twists its head 
around to the posterior end of the foot and quickly engulfs the ‘catch’, ° 
mucus and all. Turning now to the matter of plant food, snails were 
seen rasping off bits of Lemna and they seemed as well satisfied with 
dead or etiolated portions as with those which were still green. The 
way in which pond snails plow a clean path across the sides of an old 
aquarium that has become green with algal growths, is well known 
and a microscopic examination of the feces of snails reveals the 
‘presence of a large amount of plant food, green cells, diatoms, etc. 
Rathay found that Pleurococcus can pass through a snail unassimi- 
lated. A couple of green apples which had been bitten into and 
thrown into the ‘pump pool’ were later found covered, wherever the 
skin was broken, with snails that were evidently feeding. The char- 
acter of the feces of these snails furnished confirmatory evidence 
that they had eaten greedily of the apples. It is reasonable, therefore, 
to conclude from such observations that snails are omnivorous, al- 
though they are probably most attracted to plant food. The part they 
play as natural scavengers renders their presence in water troughs 
and other sources of drinking water highly desirable. 
“Some rough estimate of the amount of food ordinarily eaten by 
snails may be seen from the following experiment. A single snail, 
8 mm. in shell length, was isolated in a dish containing the usual food 
supply. After 48 hours its faeces, which are cylindrical and approxi- 
mately of equal diameter, were measured and found to give a total of 
230 mm. This means that every 24 hours a snail gets rid of over 
fourteen times its own length in feces. 
“There seems to be no evidence of any struggle for the possession 
of food among these animals. Snails will gather around a dead tad- 
pole, for example, until all the ‘standing room’ is taken and those 
that arrive late at the feast are unable to do anything aggressive. Un- 
