A new marine research laboratory on Monterey Bay in California gave Frank Mace MacFarland the ideal setting to begin, in 1892, his lifelong study of sea slugs (nudibranchs). MacFarland became a world expert on nudibranchs—colorful mollusks that have no protective outer shell, and include some 3,000 species. MacFarland’s wife, Olive Hornbrook MacFarland, worked alongside him and painted the watercolors that illustrate his publications. Many sea slugs warn away predators with striking patterns and colors that advertise their powerful chemical defenses. Some species produce their own toxins, including sulphuric acid. Others store poisons taken from prey such as toxic algae.