All of the different groups of the mollusca have their giants and their pigmies and the fresh-water mollusks are no exception to the rule. We have thus far studied the animals of normal size and the giants. Let us now turn our attention to some of the pigmies among the fresh-water snails. One of the commonest of these small mollusks is the Bythinia tentaculata, the shell of which does not exceed half an inch in length, and is formed in a graceful, tapering turret. This species, like many other European animals, has been introduced into this country and bids fair to eclipse many of the native species in the number of individuals. It probably first came over with some merchandise, which was shipped west by the way of the Erie canal. The snail, once established in the canal, has had every opportunity to spread over the entire United States. The canal is emptied every year and cleaned and the water, with its organisms, is allowed to flow into the little streams and the larger rivers and thence into Lake Ontario. From this lake this species has spread so that it is also found in Lakes Erie and Michigan, and will eventually spread over the entire northern portion of the United States. This is but one of the many examples of different species being carried by human agencies from one part of the world to another. But there are many species of these smaller fresh-water snails that are pigmies, indeed, whose tiny shells do not exceed an eight of an inch in length and which require the aid of a microscope to adequately study their delicate organisms. These minute animals live on water plants and on any submerged object. They vary from long, pointed, steeple-like shells to those which are perfectly rounded like a miniature apple. In our own country these little creatures may be found in any of our ponds or streams, and the lively little animals are well worth a closer acquaintance. They are known scientifically under the difficult names of Paludinella, Amnicola, Somatogyrus, Fluminicola, with many others, and do not bear any specific English titles. Much more might be written concerning the habits and variations of the freshwater snails. The best way to become acquainted with these interesting animals is to collect them alive and study their various modes of life in an aquarium. This receptacle need not be an elaborate or expensive affair. A fish globe six or eight inches in diameter makes an admirable aquarium and even a quart Mason fruit jar has been successfully used by the writer. The bottom should be covered to a depth of an inch or more with clean, fine sand and several stones should be introduced for the snails to “roost” upon. If the aquarium is large enough a few water plants like water cress might be introduced to assist in purifying the water.