Seligman, who had accompanied Rivers on the expedition to the Torres Sraits, observes that tortoise-shell butterflies continue to hover around the nettles on which the caterpillars of the species feed, and proposes a theory that the nutritional interest has been replaced by a reproductive one. He writes that he would like to develop the theory by testing the sex of the butterflies hovering over the nettles to verify if it is both the males and the females that do this.