Frank inquired what the Physalia was.
"You have seen it very often at sea," said Captain Johnson, "and probably you knew it as a Portuguese man-of-war."
"Oh, certainly," Frank answered. "We saw thousands and thousands of them on the Pacific Ocean when we were coming from San Francisco, and sometimes the water was covered with them for hours at a time. And they looked very pretty, with their little sails spread to catch the wind."
"What you saw above the surface was not really a sail," the captain replied, "but a little sack containing air. The Physalia has the power of contracting this sack, so that it can sink beneath the waves for protection against a storm or to avoid other dangers. The use of the long filaments is not well understood; but they are evidently for purposes of defence, as each of them contains a sting that has anything but an agreeable effect on the swimmer who comes in contact with it."
Fred asked if the Physalia was anything like the sea-anemone which he had seen in Aquarius, and had admired greatly on account of its beautiful colors.
"How many colors of it do you think you have seen?" the captain asked, in reply.
