1888.] MIOEOSCOPICAL JOUKNAL. 43 



Biology of fresli -water Sponges. — I.* 



By EDWARD POTTS. 



PHILADELPHIA, PA. 



In constitution and general appearance the fresh-water sponges resemble 

 many of those of a marine habitat, excepting in one particular. This crucial 

 point is the presence, during certain resting seasons, in most of the former, 

 and the absence from all the latter, of those ' seed-like bodies ' that have 

 been known and described by various authors under the names of ovaria, 

 gemmules, statoblasts, statospheres, sphaerulge, etc. In the past I have gen-, 

 erally avoided the use of the familiar word statoblast, as it did not seem 

 clearly proven that the function, of these ' seed-like bodies' of the sponges 

 was identical with that of the statoblasts of the polyzoa, etc. ; and have used 

 the terms statospheres, or sphaeruke, as suggesting merely their general 

 appearance. Latterlv, however, I have concurred with several European 

 writers in the use of the old term, gemmules ; the principal objection to which 

 is that with some persons the name may seem like a return to the exploded 

 vegetable theory of sponges. It is hardly necessary to sa}^ that this idea is 

 not intended. 



In shape these gemmules are nearly spherical ; they are about -gJ^ of an inch 

 in diameter, or as large as very small mustard seeds. They are found some- 

 times in continuous lavers, as at the base of encrusting sponges ; sometimes 

 they rest singly in the interspaces among the skeleton spicules ; again, they 

 occur in groups of a dozen or less, sparsely scattered through the sponge 

 mass, or in smaller, denser groups, closely enveloped in a compact cellular 

 parenchyma. Their principal coat, presumably of chitin, encloses a com- 

 pact mass of protoplasmic globules, each of which is charged with numbers 

 of discoidal particles, whose function, though all important, it is not my in- 

 tention to discuss in the present paper. A circular orifice, rarely more than 

 one, through this chitinous coat, sometimes, though inaptly, called the hilum, 

 should be known as the foramen or foraminal aperture. Through it, at the 

 time of germination, the above mentioned protoplasmic bodies make their 

 exit, crawling by an amoeboid movement, and spreading out on every side. 

 In a few^ hours the infant colony may be seen producing aqueous currents, 

 developing and arranging skeleton spicules, and in every way living the life 

 of a young sponge. The foraminal aperture is rarely plain ; more frequently 

 it is infundibular, iiaving a slightly raised and expanded margin ; while in 

 still other species it is prolonged into cylindrical or funnel-shaped tubules. 



In most species, possibly in all under normal conditions, the chitinous coat 

 is surrounded by a ' crust,' composed of air cells, often so minute as to be 

 with difficulty ' resolvable,' even with a high power of the microscope ; in 

 other species so large as to be readily discerned by the use of a low one. In 

 the first instance it has been called a ' grJinular,' in the other, a ' cellular ' 

 ' crust.' In this are imbedded the spicules which are relied on to determine 

 the generic classification of these sponges. 



To recur for a moment to the resemblance stated to exist between the fresh 

 water and some of the marine sponges, — we can see no obvious reason why 

 all the marine forms should not have their representatives among those be- 

 longing to fresh water ; but it is a fact that all of tlic latter, as yet discovered, 

 are silicioiis ; — that is, the skeleton or framework (corresponding to the elastic 

 fibre of which commercial sponges are composed), upon which the slime- 

 like sponge flesh, known as ' sarcode,' is supported, and through whose in- 

 terstices the currents meander, is composed of silicious spicules, slightly 



♦Reprint of the introduction to a monograph of the fresh-water sponges read before the Philadelphia 

 Academy, May 31, '87, 



