1884.] NATURAL SCIENCES OF PHILADELPHIA. 29 



an inch thick, of the appearance of crumbling plaster, and, as in 

 the other cases, it consisted of the sponge before named, with 

 but a small proportion of intruded material. 



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, there- 

 fore, 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 some species inhabiting exposed 

 situations toa}', of course, be broken off and destroyed while the 

 sarcode still covers them; but in the sessile portions, and in all 

 when sufficiently 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 simultaneous amoeboid 

 movements into dense groups, where thej^ are soon covered by 

 a tough chitinous " coat," which, in time, generalh' becomes 

 surrounded by a " crust " of minute granular cells, and armor- 

 plated by a series of protective spicules. These groups are now 

 recognized as the statoblasts, gemmules or winter-eggs of the 

 sponge — eggs only in appearance — in reality the resting spores 

 or protected germs which conserve the life of the individual 

 through the cold and storms of winter, and awake very early iri 

 the springtime into new life — yet a continuance only of the 

 same existence which was seen a few months before nestling into 

 this winter's sleep. 



If this is the ordinary course with these organisms there seems 

 no reason to regard them as serious causes of the pollution of 

 our streams, though violent freshets before this resting period is 

 reached may tear them to pieces, and their decay may give a 

 temporary taint to the water. 



Continuing the narrative of his exploration, Mr. Potts described 

 the iron pipes which had lain for many years upon the bottom of 

 the fore-bay, as covered in some places to the depth of an inch 

 or more, with a crust richly colored by iron-oxide, but principally 

 composed, as were the others, of the spicules and statoblasts of 

 M. Leidyi. Upon the surface of this crust in places, he found 

 the remains of large colonies of Urnatella gracilis Leidy. In 

 the absence of a\-\y positive knowledge of the winter condition of 

 this curious polyp, Mr. Potts had examined with much interest 

 a novel form of statoblast, which was frequent upon the same 

 pieces of sponge ; but he was unsuccessful in associating it with 

 the polyzoan. It is most probable that the life is continued as 

 suggested by Dr. Leid}', within the urn-like joints of this crea- 



