. Text book of zoology. Zoology. Appendisc.: Tunicata. 537 Appendix to the Vektebeata. Tunicata {Sea-Squirts). The Tunicata are a small group of marine animals, which were formerly usually regarded as Mollusca, or placed with some other division of the Invertebrata; only recently has it been demonstrated that they are most nearly allied to the Vertebrata, a relationship which is made specially clear by a consideration of their ontogeny. In particular it has been shown that in early life at least they agree with the Vertebrata in the possession of a notochord, and in the position of the central

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. Text book of zoology. Zoology. Appendisc.: Tunicata. 537 Appendix to the Vektebeata. Tunicata {Sea-Squirts). The Tunicata are a small group of marine animals, which were formerly usually regarded as Mollusca, or placed with some other division of the Invertebrata; only recently has it been demonstrated that they are most nearly allied to the Vertebrata, a relationship which is made specially clear by a consideration of their ontogeny. In particular it has been shown that in early life at least they agree with the Vertebrata in the possession of a notochord, and in the position of the central
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Image ID: RE3CXT
. Text book of zoology. Zoology. Appendisc.: Tunicata. 537 Appendix to the Vektebeata. Tunicata {Sea-Squirts). The Tunicata are a small group of marine animals, which were formerly usually regarded as Mollusca, or placed with some other division of the Invertebrata; only recently has it been demonstrated that they are most nearly allied to the Vertebrata, a relationship which is made specially clear by a consideration of their ontogeny. In particular it has been shown that in early life at least they agree with the Vertebrata in the possession of a notochord, and in the position of the central nervous system, both fundamental points. In spite of this, they are not, however, incorporated with the Vertebrates, but treated of in an appendix, because the majority undergo so peculiar a metamorphosis that the Vertebrate characters. Fig. 425. A diagram of one of the Appendioularia, viewed from the side, stretched out straight. B ditto of an Ascidian larva, a anus, ch chorda, g branchial ohamher, m mouth, n train, n' nerve cord, t gut.—Orig. have completely disappeared in the adult, which has received an entirely different impress : thus it is more convenient to consider them separately. It may also be noted here that the Tunicata, like the true Vertebrata, do not exhibit definite affinities with any of the Invei-tebrata. Insight into the characteristics of this group is best attained by a separate consideration of its various sub-divisions belonging to it. The following general characteristics may, however, be noticed : the skeleton is at best only represented by the aotochord, the nervous system is feebly developed, so also are the sense organs. The Tunicata are hermaphrodite, ovaries and testes are continued directly into their ducts. Eepreduction by budding frequently occurs. The Appendioularia possess the simplest and most easily com- prehended organisation. They are tiny, transparent, free-swimming, marine forms, with some resemblance to tadpoles. The body is. Pleas
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