Macrocilia with numerous shafts from the lips of the ctenophore Beroe

Abstract

The maerocilia are 6 to 10 /xm thick and 50 to 60 jam long. Each consists of 2000 to 3000 shafts, of the typical 9 + 2 pattern, which are arranged in a hexagonal array within a single membrane. The whole macrocilium beats like a single cilium, inward with reference to the mouth, and with antiplectic metachronal waves. Isolated macrocilia, when cut off, oscillate in one plane by a symmetrical bending movement at the middle. Cross-connexions lie between nearby fibrils of adjacent shafts in three different planes, and are apparently strong and permanent. The fibrils, each consisting of a pair of tubules, are numbered with these bridges as reference points. A system of tubules spreads between the basal bodies. Hoot structures are little developed. In bent cilia there is no buckling of shafts and the diameter of the shafts is the same on the concave as on the convex side. Therefore an active sliding mechanism between fibrils 2, 3, 4 (and between fibrils 6, 7, 8), rather than a contractile one, is postulated as the source of movement. This theory may apply to all cilia, and is an example of how this unique giant cilium may be utilized for the analysis of the function of the components of the 9 + 2 pattern during active movement.