In the summer of 1831 Henslow was offered a place as naturalist to sail aboard the survey ship HMS "Beagle" on a two-year voyage to survey South America, but his wife dissuaded him from accepting. Seeing a perfect opportunity for his protégé, Henslow wrote to the ship's captain Robert Fitzroy telling him that Darwin was the ideal man to join the expedition team. During the voyage, Darwin corresponded with Henslow, and collected plants with him in mind. In particular, when first arriving at the Galápagos Islands Darwin noted "I certainly recognize S America in Ornithology, would a botanist?", and went on to collect plant specimens carefully labelled by island and date. He also labelled the mockingbirds he caught, and initially thought these were varieties but while arranging these bird specimens on the last lap of the voyage he began wondering if they could be species, a possibility which would "undermine the stability of Species". Henslow's teaching continued to influence Darwin's work on evolution.