Bulletin Volume 82, . 1, . 1

Bulletin Volume 82, . 1, . 1

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1915 edition. Excerpt: ...would of necessity be composed of very numerous and very short columnals, for the columnals would be attached to each other not by true articulations but by loose sutures; the amount of possible accommodation at a loose suture is far less than that at a true articulation, in which an articular fulcral ridge is developed and the ligament fibers have become segregated into two bundles one on either side of it, and therefore many such loose sutures must be developed in a given length of column to do the work of a single articulation. This explanation derives the crinoid stem from the original central plate equally well with the first, while at the same time it indicates the formation of the columnals from their first inception by a continuous twinning or reduplicative process, each columnal being formed by an original ossification of the same type and in the same place, thus making each individual columnal, as well as the entire column, the equivalent of a single calyx plate--a state of affairs which, so far as we can see, is probably very near the truth. From what we know of the formation and development of the columnals in the recent crinoids it would appear that they are derived from an apical calyx plate after the phylogenetical formation and fixation of that plate, in other words, after the perfection of the skeletal investment of the calyx. Moreover it is only by such a supposition that we are able to bring into phylogenetical agreement and to reduce to a common and logical starting point such diverse apical conditions as are found in Marsupites and Uintacrinus, Holopus, the pentacrinites and the comatulids. But there is another possibility which, however remote, should not be overlooked. The apical area of the crinoidal ancestor may have been...show more

Product details

  • Paperback | 168 pages
  • 189 x 246 x 9mm | 313g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236634365
  • 9781236634368