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Besides these animals, six varieties of Pteropodes were caught; also a Glaucus, differing from that of the Atlantic Janthina penicephala Per., a Planaria, Salpa vivipara Per., a Pyrosoma, resembling that of the Atlantic, and a Lepas, attached to the shell of the Janthina. Our collection of Acalephi was extremely rich; of fourteen kinds taken, only one, Physalia Lamartinieri, was known to us.
When I went on deck at night, I observed a change in the appearance of the constellations; and now the beautiful one of the Southern Cross became every day clearer, rising as it were in the sky. The magellhenic clouds also came in sight, showing that the ship was now in the southern hemisphere. Frequently patches of light were passed in the water; caused, Mr Hooker told me, by the pyrosoma.
If we come now to consider the more partial phosphorescence of the sea, we find that it is due to animals belonging to almost every group of marine forms to Echinoderms, or creatures of the sea-urchin and star-fish type, to Annelid worm, to Medusidæ, or jelly-fish, as they are popularly called, including the "great domes" and the "silvery disks" of the passage above quoted from Professor Martin Duncan, to Tunicates, among which is the Pyrosoma, to Mollusks, Crustaceans, and in very many cases to Actinozoa, or forms belonging to the type of the sea anemone and the coral polyp.
It was like a great sac, with its walls of jelly about an inch in thickness. It was four feet long and ten inches in diameter. When a Pyrosoma is stimulated by having its surface touched, the phosphorescent light breaks out just at the spot stimulated, and then spreads over the surface of the colony to the surrounding animals.
Moreover, these forms are almost without exception compound. Like the Pyrosoma, they have a common life belonging to a whole stock or colony, as well as an individual life. Now, throughout this sub-division of the Actinozoa phosphorescence is a very general phenomenon.
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