Customarily, the ship's surgeon took the position of a naturalist, and "Beagle" surgeon Robert McCormick sought fame and fortune as an explorer. When they first met at the start of the voyage, Darwin had commented that "My friend is an ass, but we jog on very amicably". They walked into the countryside of St. Jago together, and Darwin, influenced by Lyell, found the surgeon's approach old-fashioned. They found a remarkable baobab tree, which FitzRoy measured and sketched. Darwin went on subsequent "riding expeditions" with Benjamin Bynoe and Rowlett to visit Ribeira Grande and St Domingo. FitzRoy extended their stay to 23 days to complete his measurements of magnetism. Darwin subsequently wrote to Henslow that his collecting included "several specimens of an Octopus, which possessed a most marvellous power of changing its colours; equalling any chamaelion, & evidently accommodating the changes to the colour of the ground which it passed over.—yellowish green, dark brown & red were the prevailing colours: this fact appears to be new, as far as I can find out." Henslow replied that "The fact is not new, but any fresh observations will be highly important."