A. Lateral view of a normal male in 20 mM serotonin. Note the tight ventral-inward curl of the tail. The head is to the up and to the right. Scale bar, 100 um.

B. Tail curling as a function of serotonin concentration. The y-axis indicates the percentage of males curled >50% of the time plotted against the concentration of serotonin (mM) in M9 buffer (see Materials and Methods). Points at zero serotonin are shown on the Y axis. Number of worms per point: wild type (43-108, total n= 523), unc-29 (17-70, total n= 305), (11-28, total n= 138). Symbols: solid circles - wild type; open circles - unc-29; open triangles - unc-49.