XOOLOGY. 593 



ation the size aud exterior appearance of the spiculae remaining as be- 

 fore, the liardly noticeable channel has become a wide caual, open at 

 both ends, aud occai)ying more than one half of the breadth of the spi- 

 cule. This does not occur merely in occasional instances, but univer- 

 sally throughout the fragment of sponge so affected. 



" The birotulate sjiicules of this si)onge also are short and of a pecu- 

 liarly substantial apijearauce, with entire reflexed margins, yet in the 

 l)reseut preparation they could with difficulty be detected as mere ghosts 

 of their normal shapes. The two discs rarely remained together, their 

 characteristic entire margins were gone, the rotules being represented 

 merely by a line of very tine rays." {Proc. Acad. Nat. Sc. Phila., 1884, 

 pp. 184-185.) 



Fresh-water sponges and water pollution. — It has been stated that 

 fresh-water sponges, in their decay, are a notable source of ])ollution 

 of drinking-waler, and that the sui)ply thereof derived from the reser- 

 voirs may be materially injured by them. Mr. Edward Potts has taken 

 measures to inquire into the truth of these allegations. In the month 

 of February, 1884, he examined '' the fore-bay at Fairmount Water- 

 works, on the Schuylkill Eiver", when the water had been temporarily 

 withdrawn. He found, on the bottom and sides, wherever he could get 

 within reach, and as far as his eye could detect in other i)laces, the 

 surface "covered by a mud colored incrustation of considerable thick- 

 ness, which a more minute examination showed to be composed almost 

 wholly of statoblasts and spicules of the sponge Meyenia Leidyi,''^ which 

 was the prominent one. Some few remains of Meyenia fiuviatilis and 

 SpongiUa fragilis were also seen. 



" While considering the effect of the presence of so large a sponge 

 growth at the very inlet to the supply pumps, Mr. Potts stated that this 

 particular species was conspicuous among the known North American- 

 sponges by its great relative density and the small proportion of its 

 sarcode or flesh. Its decay, therefore, at the termination of its period 

 of summer growth would be a less cause of pollution to the water-supply 

 than that of any other sponge. 



"Moreover, from recent investigations into the life history of these 

 low organisms, he was inclined to believe that decay was not the normal 

 or necessary result of the close of each season's growth. The fragile 

 branches of son)e species inliabiting exposed situations may, of course, 

 be broken off and destroyed while the sarcode still covers them; but 

 in the sessile portions, and in all when suffioiently protected, the cells 

 of the sarcode at the period of full maturity, forsaking their places 

 along the lines of the skeleton framework, gather together by simulta- 

 neous ama^boid movements into dense groups, where they are soon 

 covered by a tough chitinous ' coat,' which, in time, generally becomes 

 surrounded by a 'crust' of minute granular cells, and armor plated by 

 a series of protective si)icules. These groups are now recognized as 

 the statoblasts, gemmules or winter eggs of the sponge — eggs only in 

 S, Mis. 33 38 



