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In strong current, sponges will attain perhaps three to five times greater size,and yet they will retain their normal shape. An old sponge tends to have a doughnut shape. FROST: A difficulty there, is to distinguish between direct and indirect effects of external currents. By indirect, I mean the physical transport of materials such as metabolites and detritus from the area of the sponge, and current effects making higher concentrations of food particles available. I am interested in the direct effect of that current on the filtering rate of the sponge.

In sponges there is a whole membrane system which develops, the silicalemma. There is no indication at all of involvement of any silicon accumulation any place other than inside the silicalemma. This means that the silicon is pumped in, unpolymerized, and polymerization occurs after passage across the silicalemma. The diatom group can synchronize the cells and look at the stages of silicon deposition. They have introduced the use of germanium in looking at silicon deposition, because ger­ manium acts as a competitive inhibitor of silicon transport.

A few marine sponges, which do not produce gemmules, regress during the winter to a simplified form of reduced size lacking flagellated cham­ bers (Hartman, f 58; Simpson, f 68; also see Stone, f 7 0 ) . The dormant form of these sponges is analogous to gemmules in many respects. Even when there is no true dormancy the rate of growth and presumably the rates of other processes may vary seasonally, especially in temperate regions (see Wells, Wells and Gray, f 6 4 ) . Most marine sponges remain more or less active throughout the year, and some of them may live for many years (Reiswig, f 73; Dayton, Robilliard, Paine and Dayton, '74).