BULLETIN OF THE UNITED STATES FISH COMMISSION. 389 



C5.-FRESM WATER SPONGES: WHAT, WHERE, WHEN, AIV» WHO 



W ANTS THEM. 



By EDWAKD POTTS. 



The purpose of this article is to give to the uninitiated some idea of 

 the appearance of fresh-water 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 organ- 

 isms, 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 bor- 

 der 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 observ- 

 ers 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 struct- 

 ure or frame- work does not consist, as in the familiar marine sponges of 

 commerce, of an elastic net-work of tough fibers — but of lines of fasci- 

 culated flint-needles, about one j^q 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 nol 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 incrusta- 

 tions of varying size and shape, and 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 Confervas occasion- 



