digestive cavity. Such beings as the Campanula produce, through budding, beautiful little jelly-fishes, which swim freely about. They in their turn produce eggs, from which spring the stationary colonies of Hydrae. There is an alternate generation, Campanulariae producing jelly-fish, jelly-fish producing Campanulariae. We see the Hydra living as an independent organism—the Hydra of our fresh-water ponds—and in a transitory stage, as the Campanula. Sometimes a colony of these Plydroids form a freely swimming organism, as the Portuguese man-of-war. The Ctenophorae, or comb-bearing jelly-fishes, pure as crystal and transparent as glass, are characterized by their organs of motion, which are eight delicate combs, by the graceful movement of which the Beroes and Cydippe glide through the sea. They are intermediate in some respects between the Anemones and common jelly-fish (Aurelia). By glancing at Tree II. we see the probable origin of the Anemones, Corals, and Jelly-fish in the Sponges, the Anemones and Corals coming from the hard sponges, the fossil forms of which, like Ventriculites and Guettardia (Figs. 13, 17), closely resemble in the arrangement of their chambers those of the Anemone and Coral. By comparing the transverse section of a sponge (Fig. 22) with that of the jelly-fish (Fig. 21), we see that the canals of the sponge are the same as those of the jelly-fish, though more simple in their arrangement. Though objections have been, and will be, raised to this view of the origin of the Actinozoa and Hydrozoa, that they have so descended from stationary beings the Anemones and Hydroid polyps are the living proofs. That these stationary ancestors were sponges, or beings allied to them, is rendered very probable by the harmonious evidences of the structure, development, and fossil remains of the entire group.
We will now leave the Coelenterata, considered as a distinct division of the animal kingdom on account of its
