One purpose of this chapter is to give to the uninitiated some idea of the appearance of freshwater sponges; to suggest where they should be looked for and when it is best to collect them.

It seems to be a fact that very many persons, not excepting some of scientific tastes, are unaware of the existence of sponges in our fresh waters. This may be partially explained by the further fact that in England, and throughout Continental Europe, the keen eyes that for years past have been searching every body of water for its minuter organisms, have thus far failed to discover and describe more than two species of sponges. The zeal, therefore, enlisted in the search for them has been far less than the puzzling character of their organization - upon the border land of animal and vegetable life - and the beauty and quaintness of form of some of their component parts would seem naturally to invite. It is to be hoped, however, that the far richer fauna which has already been developed in America, with the strong probability of a considerable increase in genera and species in the near future, may stimulate observers to aid in this interesting work.

It is not the present intention of the writer to give either a scientific or popular description of these sponges; but only by a few words to help those whose interest may be awakened in the subject, to seek them intelligently and to recognize them when found.

First, then, all fresh-water sponges which have been described at the present date are of a silicious character; that is, their skeleton structure or frame-work does not consist, as in the familiar marine sponges of commerce, of an elastic network of tough fibres - but of lines of fasciculated flint-needles, about one one-hundreth of an inch in length, so arranged as to form a loose intertexture, penetrated by canals, and supporting the sponge-flesh. When crushed, therefore, this texture is permanently destroyed and will not resume its original shape. The sponge-flesh, so called, is a thin slime covering the spicules and lining the canals of the living organism having a peculiar and not unpleasant odor, when fresh, but betraying its animal nature by an extremity of foulness when the dead sponge has been kept a few days in water.

Many of the species, native in this country, appear as mere incrustations of varying size and shape, and are from less than a line to an inch or more in thickness. Their surface, smooth, or more or less tuberculated, is, in some species, supplemented by a higher growth of branches or finger-like processes, frequently several inches in length. In color they vary from nearly white to the most vivid green, in an almost exact ratio to the degree of light received. The slimy growth of Convervae occasionally seen upon the bottom of pools and streams, or dense masses of water-moss, may momentarily mislead the collector; but a pocket lens will reveal to him at a glance the minute leaves of the moss, or the delicate green threads of the algae; while in the true sponge he will hardly fail to see the characteristic pores penetrating its surface and to detect the fine points of numerous projecting spicules.

The particular feature distinguishing freshwater from marine sponges is the presence in the former, when mature, of the reproductive bodies known as statoblasts or stato-spheres. These are nearly spherical, light or dark brown, generally easily visible by the naked eye, and occupy positions at the lower surface or throughout the mass of the sponge. They should be carefully looked for and gathered with the specimen, as it is upon the form of the spicules encrusting their surface, that the classification of fresh-water sponges principally depends. Either very early or very late in the season minute groups of these statospheres may often be found, unaccompanied by the skeleton spicules and slime-like flesh of the sponge, and it is well worth while to gather and preserve them.

These sponges are found growing upon any supporting substance except mud, and at every depth beneath the surface of the water; but they affect chiefly the under and upper surface of stones and timbers, the sides of piling, and of submerged stumps and branches. The stems and roots of water plants are often coated and matted together by them. As the silting of earthy matter into their pores would soon suffocate them, we find in standing pools the most flourishing specimens attached to the under side of stones or waterlogged timbers, which shield them from the intru.