SPONGES. 389 



its surface and highest orifice with water. On strewing 

 some powdered chalk on the surface of the water, tho 

 currents were visible to a great distance ; and on placing 

 some pieces of cork or of dry paper over tho apertures, I 

 could perceive them moving, by the force of the currents, 

 at the distance of ten feet from the table on which tho 

 specimen rested." 



Dr. N. Lieberkiihn, in his valuable contributions to 

 the History of the Development of the Spongillce, observes 

 that with regard to the skeleton of /S y . fluviatttis, the 

 spicules are not united at the base by a siliceous material, 

 as stated by Meyen, but by a substance destructible by 

 heat. The spicules are usually arranged in aggregate 

 bundles, which meet point to point at an obtuse angle, and 

 project slightly above the surface of the sponge. Minute 

 portions of the gelatinous substance exhibit under the 

 microscope amoeba-like movements, respecting which it is 

 unknown whether they are vital phenomena, as supposed 

 by Dujardin, or referable to a process of decomposition. 1 



The living spongillae are often seated, not immediately 

 upon the wood, stone, &c. upon which they may be 

 growing, but separated from it by a peculiar dark-brown 

 substance often several inches thick. This mass is com- 

 posed chiefly of the remains of the dead sponge, empty 

 gernmulc- cases with their amphidiscs, various forms of 

 siliceous spicules, &c. ; and occasionally there may be 



(1) The motile phenomena hitherto. observed in sponges are connected with 

 larger or smaller portions of the external integument, and of the exhalent 

 tubules, or with isolated cells. When the exhalent tubules of Spongilla con- 

 tract, their walls become shortened and thickened, and the previously smooth 

 surface uneven, from the presence of the spherical cpntracted cells, whose 

 outlines at the same time are rendered very distinct, whilst they were before 

 invisible, or at most here and there perceptible. Other motile phenomena are 

 witnessed when a Spongilla with external membrane and exhalent canals is 

 produced from a cut-off portion. The fragment thus cut off may be so thin as 

 to consist of only a single layer of retictilar parenchymatous fibres. The inter- 

 stitial rounded, oval, or irregular spaces, under these circumstances, become for 

 the most part closed, owing to the gradual increase in breadth of the trape- 

 culye, or cavities may be left when their membranes are stretched over them 

 only from the upper and under sides of the trabeculse, which enclose a space 

 between them, and may become portions of the outer membrane with exhalent 

 canals. It cannot be determined with certainty to what extent this change of 

 <brm is connected with any multiplication of cells. Lastly, movements in the 

 individual cells have been noticed, the globular cells becoming stellate, and the 

 stellate ones globular in turn, but without any locomotion. This phenomenon 

 occurs, not only in the cells of the uninjured substance, but also in those which 

 have been detached. N. Leiberkiihn, "On the Motile Phenomena in Sponges," 

 Micros. Journ. vol. iv. 1864, p. 189, and Journ. Micros. Science, vol. v. 1857, p> 

 SU, "On the Development of the Spongilloe." 



