


OUR FRESH-WATER SHELLS. 649 
the complete development of the egg into a little snail, may 
be easily watched with a common magnifier. When nothing 
more than a cluster of cells may be defined within the egg, 
this mass is seen to slowly and continually revolve within. 
Soon two little eyes make their appearance, and by suc- 
cessive stages the shell is formed, and with a high magnifier 
the little one may be seen eating its way through the egg- 
shell and mucous which surrounds it. 
These snails have the power of crawling or floating along 
the surface of the water, the creeping disk being just level 
with the surface and the shell hanging beneath. When they 
wish to sink, a portion of the air contained in the lung 
cavity is expelled, and a slight clicking sound is heard ac- 
companying this movement. They are mostly vegetable 
feeders, and seem to live on the ooze and slime that cover 
the stones and aquatic plants of their abode. 
There is one little species that seems more like a land 
snail in its habits, from the fact that it can live a long time 
without immersion in water. It is generally found in little 
pools, where the water stands only a portion of the year. 
During the dry season it hibernates like the land snails by 
plugging up the aperture of the shell with a thin partition 
Of a viscid secretion of the animal, and in this condition 
will survive the droughts of summer. 
A simple and serviceable collecting apparatus can be made 
from a tin dipper fastened toa pole six or eight feet in 
length. The bottom of the dipper should be made of wire 
netting. With this one cau scoop along the bottom of ditches 
and ponds, and will be rewarded by finding many a curious 
Shell. And if he is at all interested in insects he will turn 
up some singular looking monsters in miniature, that will 
turn out to be the larval state of dragon flies or other well 
known forms. Even without the dipper the collector may 
find many species by examining the bits of bark and stone 
and the stems of aquatic plants that he may pull up from 
the pond. The under side of dn also proves a resting 
AMER. NATURALIST, VOL. III. 
