54
THE ESSEX NATURALIST.
than some raised as singles. This suggests that the weight of
snails is approximately the same whatever number be reared in
a jar. Table 2 shows an experiment in which this was tried and
proved to be so.
Table II.
Hence the weight of each snail varies nearly in inverse pro-
portion to the number in the jar, and the total weight of all the
snails in a jar, except S.25, is approximately the same.
Prof. Boycott and I both thought during our first three years'
work that a large jar was necessary to rear snails to maturity
and that they could not be successfully reared in jars of the two
smaller sizes. I have since found that this is not so, but it
remains true that using Elodea as weed they regularly mature in
large jars and only very exceptionally in the smaller. They
appear, however, never to feed on Elodea, except sometimes on
decayed leaves or stems, while they eat lettuce and watercress
readily. They also never feed on Lemna, Spirogyra, nor on several
of the filamentous algae which grow in my jars. But if given
lettuce or water cress they may be reared and breed as easily in
small jars as big, and grow to as large a size. I have reared 108
thus in the last two years. If, however, lack of food is the sole
cause one would expect to be able to get two snails in a jar to
grow as quickly as one ; or since this occasionally happens in
ordinary routine it is better to try three snails to one. But up
to the present even with food added, I have not got three snails in
a jar to grow as rapidly or to as large a size as one. The explana-
tion may be that the food factor is not the only one involved in