As the sponge grows it frequently attaches itself to small molluscs such as the young of _Vivipara bengalensis_, which finally become buried in its substance and thus perish. Possibly their decaying bodies may afford it nourishment, but of the natural food of sponges we know little. _S. carteri_ flourishes best and reaches its largest size in ponds used for domestic purposes by natives of India, and thrives in water thick with soap-suds. It is possible, though direct proof is lacking, that the sponge does good in purifying water used for washing the clothes, utensils, and persons of those who drink the same water, by absorbing decaying animal and vegetable matter from it. Various minute algæ are found associated with _S. carteri_, but of these little is yet known. The green flush sometimes seen on the surface of the typical form is due to the fact that the superficial cells of the parenchyma contain green corpuscles. These, however, are never very numerous and are not found in the inner parts of the sponge, perhaps owing to its massive form. It is noteworthy that these green bodies flourish in large numbers throughout the substance of sponges of _S. proliferens_, a species always far from massive, growing in the same ponds as _S. carteri_. 9. Spongilla fragilis, _Leidy_. _Spongilla fragilis_, Leidy, P. Ac. Philad. 1851, p. 278. _Spongilla lordii_, Bowerbank, P. Zool. Soc. London, 1863, p. 466, pl. xxxviii, fig. 17. _Spongilla contecta_, Noll, Zool. Garten*, 1870, p. 173. _Spongilla ottavænsis_, Dawson, Canad. Nat.* (new series) viii, p. 5 (1878). _Spongilla sibirica_, Dybowski, Zool. Anz., Jahr. i, p. 53 (1878). _Spongilla morgiana_, Potts, P. Ac. Philad. 1880, p. 330. _Spongilla lordii_, Carter, Ann. Nat. Hist. (5) vii, p. 89, pl. vi, fig. 13 (1881). _Spongilla sibirica_, Dybowski, Mém. Ac. St. Pétersb. (7) xxx, no. x, p. 10, fig. 12. _Spongilla glomerata_, Noll, Zool. Anz., Jahr. ix, p. 682 (1886). _Spongilla fragilis_, Vejdovsky, P. Ac. Philad. 1887, p. 176. _Spongilla fragilis_, Potts, _ibid._ p. 197, pl. v, fig. 2; pl. viii, figs. 1-4. _Spongilla fragilis_, Weltner, Arch. Naturg. lix (1), p. 266, pl. ix, figs. 18-20 (1893). _Spongilla fragilis_, _id._, Arch. Naturg. lxi (i), p. 117 (1895). _Spongilla fragilis_, _id._, in Semon's Zool. Forsch. in Austral. u. d. Malay. Arch. v, part v, p. 523. _Spongilla fragilis_, Annandale, P. U.S. Mus. xxxvii, p. 402 (1909). _Spongilla fragilis_, _id._, Annot. Zool. Japon. vii, part ii, p. 106, pl. ii, fig. 1 (1909). _Sponge_ flat, lichenoid, never of great thickness, devoid of branches, dense in texture but very friable; colour brown, green, or whitish; oscula numerous, small, flat, distinctly star-shaped.