. Contributions to the natural history of the United States of America. Zoology; Chelonia (Genus); Ctenophora; Cnidaria; Animals. 84 ACALEPIIS IN GENERAL. Part I. Flij. 49. as Hflix witli its iAnAX is an animal of the same order as a Limax with a rmli- mentary shell, or a Tebennophorns ^vithout any shell. Similar differences occur among the Ilydroids proper in the genera Coryne, Tubularia, Canipanularia, and Sertulavia. In Porpita, we oljserve the same relations between the primary enlarged Hydra with its tentacles and the secondary fertile Ilydra^ as in Yelella. The poly- morphism in these tw
. Contributions to the natural history of the United States of America. Zoology; Chelonia (Genus); Ctenophora; Cnidaria; Animals. 84 ACALEPIIS IN GENERAL. Part I. Flij. 49. as Hflix witli its iAnAX is an animal of the same order as a Limax with a rmli- mentary shell, or a Tebennophorns ^vithout any shell. Similar differences occur among the Ilydroids proper in the genera Coryne, Tubularia, Canipanularia, and Sertulavia. In Porpita, we oljserve the same relations between the primary enlarged Hydra with its tentacles and the secondary fertile Ilydra^ as in Yelella. The poly- morphism in these two genera extends only to a marked difference between the primary Hydra and the secondary Hydr;x), analogous to the difference there is between the sterile and fertile Hydra) in Campanidaria. (Compare Firj. 15, p. 4(3.) Both Velella and Porpita acqiure their full size Ijcfore Medusae buds ap])ear upon their fertile Hydra?. In Physalia, the connnunity is also fbrnied up<ni an enlarged primary Hydra. The young of this genus has been descril)ed and figured by Huxley in two different stages of growth (Oceanic Hydrozoa, PI. X. Figs. 1 and 2). In the earliest stage it is a simple Hydra, with a single tentacle {Fir/. 1); and while that primary Hydra is enlarging and assuming its permanent character- istics, other secondary Ilydra^ somewhat different from the first, bud forth from it, and form with it a Ilydrariiuu [Fly. 2), gradually enlarging ])y the addition of others. But there is this difference Ijetween such a Physalia Ilvdrarium and a Velella Ilydrarium, that in the former the successive secondary Ilydra? differ among themselves greatly, — some acquiring a consideraljle size and having a large tentacle, while othei's remain small and have a small tentacle, and the proboscis of some having an open mouth, while in others it remains closed. But, as I shall show hereafter, similar differences are also observed among the Hydroids jiroper; so that the pecidiarities noticed in the
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