The Biological Bulletin Volume 7

The Biological Bulletin Volume 7

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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. 1904 edition. Excerpt: ...The sections were stained with Delafield's hematoxylin, followed by picric alcohol, according to the method of Stevens ('01). The picric alcohol stains the granules in the endoderm cells bright yellow, and thus makes the difference between ectoderm and endoderm cells distinct. Method Of Closure. As the result of the splitting, the stems were divided into partcylinders of various sizes, some almost complete, others with a mere strand of coenosarc; while in some, an oblique split produced pieces nearly complete at one end and very small at the other. The method of closure seems to be independent of the size of the piece, the same general process being followed in all pieces. The cut leaves a free edge of both ectoderm and endoderm. In sections of pieces which had been killed five, ten or fifteen minutes after the splitting, the endoderm cells had rounded up over the ectoderm, probably as a result of disturbing the osmotic pressures (Fig. A). The first step towards closure of the tube is the pushing of the ectoderm over the endoderm (Fig. B). Whether this is accompanied by any activity on the part of the endoderm cannot be stated definitely, but it seems probable from some sections and from what occurs in later stages, that the endoderm cells change their shape, their outer ends next the ectoderm becoming broader and the inner ends becoming pointed, the cells thus taking on a triangular rather than a rectangular shape in section. This is shown in Fig. D. Some sections, however, do not show this at all, and we must conclude, that in some cases the endoderm lags a little behind the ectoderm. During the subsequent process of closure, the ectoderm and the endoderm stretch across from both sides till they meet and form a two-layered membrane which closes...show more

Product details

  • Paperback | 98 pages
  • 189 x 246 x 5mm | 191g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236625706
  • 9781236625700