Just a tether to a power supply. But look at the copper traces for the yet to be made leg-sensors, and the four unused 3 mm holes in the upper frame. The Spider has been designed to carry any combination of brain and on-board power supply that will fit on a 12 x 6 cm pcb. The fist one I will use is the AT90S1200. It is satisfied with less than 2 mA at 3 V when active and has a serial interface for programming while in-circuit.
Weight watching The only real constraint is weight.
While the spider walks reasonably well at an all-up weight of 158 grams, performance increases as the weight goes down. On the photo above you see 92 grams. But since I want performance in normal Dutch weather, I intend to use two NiMH rechargeables, giving 2.4 V and 70 mAh each. There may be a solar cell to reacharge them. That means using a pertinax pcb, nylon M3's for mounting, and whatever else adds lightness.