This is chiefly manifested when they are pursuing a fish for food; then, if the fish endeavours to escape, they pursue him in their hunger down to deep waters; but, when the return swim is getting too long, they hold in their breath, as though calculating the length of it, and then draw themselves together and shoot up like arrows, trying to make the long ascent rapidly in order to breathe, and in the effort they spring right over a ship's masts if a ship be in the vicinity.