Advances in Methods of Teaching Zoology Volume 4, No. 1

Advances in Methods of Teaching Zoology Volume 4, No. 1

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1899 edition. Excerpt: ...no means necessarily follows that such secondary effects should manifest themselves in exactly the same fashion in different classes or even orders, indeed it would be strange if they did. Finally, MEAD has made the interesting discovery in Amphitrite that' with the exception of small areas in the immediate vicinity of the mouth the entire trunk forms from 2d. In Chiton the trunk in its early stages is almost as extensive as in this Annelid but at least one half of it is formed from the third quartette which in Annelids remains of small size. VII. History of the Third Quartette. 1. Early Cleavages and Later History. The history of the third quartette is the simplest and least varied in the development of the ectoblast. At its first division it produces the third quartette stomatoblasts whose fate is considered on page 51. To the remaining products attention will here be directed. Their first division is meridional, the spindle being horizontal, and as a result two cells of the same size are produced in each quadrant. In this and the succeeding cleavages of this quartette the posterior quadrants are the first to show signs of division. However, their acceleration is at first not of much consequence as a glance at Fig. 20 will show. The next division is at right angles to the first and affects all the cells produced by the above division (Figs. 26, 27). As in the preceding case the result is an equal cleavage in each cell making a quadrangular group of four cells in each quadrant. The acceleration of cleavages is here more marked (Fig. 27). The next cleavage occurs in the upper cells in each group (Fig. 30) and is later followed by the lower products (3 a1-1-2, 3a1-9-2 etc.). The spindles of both these cleavages are horizontal and are...show more

Product details

  • Paperback | 168 pages
  • 189 x 246 x 9mm | 313g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236754670
  • 9781236754677