. Amphioxus and the ancestry of the vertebrates [microform]. Vertebrates; Chordata; Fishes; Ascidiacea; Vertébrés; Cordés; Poissons; Ascidiacés. W'i IV. THE ASCIDIANS. The Ascidians, Tunicates, or sea-squirts, as they arc indifferently called, constitute one of the most clearly defined and yet most heterogeneous groups of animals which it is possible to imagine. There is a great variety of families, genera, and species occurring all the world over, and in all depths of the ocean from the tide-marks to the profoundest depths. Most of them are sedentary animals, remaining fixed all their lifetim

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Image ID: RJ1762
. Amphioxus and the ancestry of the vertebrates [microform]. Vertebrates; Chordata; Fishes; Ascidiacea; Vertébrés; Cordés; Poissons; Ascidiacés. W'i IV. THE ASCIDIANS. The Ascidians, Tunicates, or sea-squirts, as they arc indifferently called, constitute one of the most clearly defined and yet most heterogeneous groups of animals which it is possible to imagine. There is a great variety of families, genera, and species occurring all the world over, and in all depths of the ocean from the tide-marks to the profoundest depths. Most of them are sedentary animals, remaining fixed all their lifetime on one spot, whether attached to rocks, stones, shells, or sea-weeds, from which they are incapable of moving. There are, however, several very extraordi- nary genera of Ascidians which swim or float about per- petually in the open ocean, and have become adapted in the extremest manner to a purely pelagic environment. These pelagic Ascidians have become so modified in adap- tation to their oceanic existence, and their development diverges, as a rule, so much from the normal, that they will hardly enter at all into the present discussion, with the exception of one family, the AppcndicularicB. Just as there are two kinds of sessile Ascidians, simple and compound or colonial, so there are two analogous kinds of pelagic Ascidians. In some of the latter, however, where there is an alternation of generations, one genera- tion, namely, the asexual generation, is a solitary form, while the sexual generation is a colonial form, as, for example, the solitary Salpa and the chain-Salpa. i8o. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.. Willey, Arthur, 1867-1942. New York; London : Mcmillan

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