1. High speed cinefilms of a serpulid trochophore, a bdelloid rotifer, and an echinopluteus show two ways cilia remove particles from suspensions.2. In the pluteus a particle passing through the band of cilia triggers a localized change of beat which appears to be a reversal and which retains the particle on the upstream side of the band of cilia. Retention of particles by an induced local reversal of beat implies that the stimulus occurs during the forward effective stroke of a cilium and that the reversed effective stroke of this cilium or its neighbors begins before the forward stroke is completed. For this system, clearance and transport of particles, rejection of particles, and swimming can be accomplished by a single band of cilia.3. In the bdelloid rotifer, and probably in the serpulid trochophore, the opposed action of parallel preoral and postoral bands of cilia apparently causes the longer preoral cilia to push particles relative to the water during the latter part of the effective stroke. This system has the preoral band of cilia function in clearance and swimming, the postoral band in clearance and rejection, the food groove cilia in transport of particles.4. These two clearance mechanisms may be of wide distribution. Echinoderm larvae and the tornariae of hemichrodates appear to employ the induced local reversal of beat. The trochophores of annelids and echiuroids, veligers of mollusks, entoproct larvae, and bdelloid and flosculariacean rotifers appear to employ the system with two opposed bands of cilia.5. Clearance rates can be estimated from velocity of particle movement, length of cilia, and length of ciliated band.6. Variations in ciliation in these two feeding systems are discussed in terms of differences in clearance rates and the size range of particles cleared from suspension.7. Factors which may inherently limit clearance rate are also discussed.