Fig. 3. The effects of tetrodotoxin (TTX; black bars) compared with the control period (white bars) on frequency (A), interval (B), distance (C) or velocity (D) of anterograde contraction waves at 4 and 7 d.p.f. Values are means ± s.e.m.; for N, see Table 2). Neurons do not seem to be necessary for the initiation and progress of anterograde contraction waves before the first feeding as TTX did not affect either of the parameters at 4 d.p.f. At 7 d.p.f., however, after the theoretical time for onset of feeding, TTX reduced frequency and distance (A,C), whereas interval and velocity were unaffected (B,D). Distance (C) increased while velocity (D) decreased when comparing 4 and 7 d.p.f. larvae. *P<0.05.