Evidence of the weathervane mechanism A , Relationship between bearing of NaCl peak and curving rate. B , Same as in A except that data from animals tracked on NaCl-free assay plates were used. The line is slightly shifted to the negative value. This is because each animal has a systematic bias of curving rate and the data set included more worms with negative bias. C , Relationship between NaCl gradient in normal direction and curving rate. D , Same as C except that data from animals tracked on NaCl-free assay plates were used. E , Relationship between NaCl gradient in tangential direction and curving rate. F , Relationship between NaCl concentration change (dC/dT) and curving rate. G , Schematic representation of the pirouette mechanism. H , Schematic representation of the weathervane mechanism. In G and H , the shading indicates NaCl gradient.