Fig. 5. Stereomicrographs (A–D) and changes in diameter (E) of the tip and base of the osculum (at positions indicated by arrows in A) during contraction of the osculum. (A) Immediately after stimulation by agitation, (B) during the contraction phase when its base is fully inflated, (C) fully contracted; and (D) when relaxed at the end of the cycle; insets show enlargements of the position of the apical pinacoderm. Scale bar, 1 mm. A–D correspond to phases a–d, respectively, in (E). Between A and D the canals inflate and the apical pinacoderm raises. The wave of contraction propagates from base to tip, a distance of 1473 µm, in 12 s, a rate of 122.8 µm s^–1. Bars denote ± s.e.m. of an average of three measurements from one sponge. (Movie 4 in supplementary material.)