The External Opening of the Brick-Red Gland in Limulus Polyphemus

The External Opening of the Brick-Red Gland in Limulus Polyphemus

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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. 1898 edition. Excerpt: ...' Essential similarity in origin and fate will be considered a sufficient criterion of the homology of cells, as it is, by common consent, of tissues and organs. That the cleavage cells in the forms under consideration are similar in origin is obvious, and is implied by the fact that they constitute a well-defined type of cleavage; but whether they are alike in destiny is more difficult to ascertain. The products of the two divisions of the oocytes--the polar globules--correspond in origin and destiny. The cleavage proper may be " equal " or " unequal." a. E gual cleavage. Hatschek followed the equal cleavage of Eupomatus in detail to sixteen cells, and Wilson describes that of the related H_ya'roz'a'es to thirty cells. The observations on Lepidonotus recorded in the previous chapters agree precisely with these, and have been extended to the later cleavage. The first cleavage furrow is always vertical, but in unequal cleavage the two resulting cells vary more or less in size. The larger size of one product is a means of orientation, and since in all cases it possesses certain potential peculiarities, it may be considered in a general way homologous among eggs of this type. Is the larger size of the cell the cause of its peculiar destiny (according to the law of progressive differentiation), or is the peculiar destiny the cause of its larger size (precocious segregation of embryonic material and specific cell organization)? The answer to this question depends upon whether one of the two cells in equal cleavage is homologous with the larger cell in unequal cleavage. This is the immediate problem to be solved by the study of equal cleavage. In this type the two blastomeres divide into four cells of more

Product details

  • Paperback | 64 pages
  • 189 x 246 x 3mm | 132g
  • United States
  • English
  • black & white illustrations
  • 1236965418
  • 9781236965417