Fig. 1. (A) Illustration of the apparatus for the temperature gradient and set-up of an agar plate for behavior assays. (B) Temperature gradients on an aluminum slab and an agar plate. A temperature gradient was produced on an aluminum slab, and temperatures of surfaces of the slab (open circles, broken line) and an agar plate placed on it (crosses, solid line) were monitored at various positions, as described in the Materials and methods section. The means (± S.D.) of temperatures obtained in 19 experiments are shown.