Sinopsis
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. 1894 edition. Excerpt: ... blastomeres almost conventional outlines; it is only after the fourth cleavage that variations are observed. In Acipenser, on the other hand, segmentation is holoblastic, although the furrows traversing the yolk region are of an exceedingly superficial character.1 The consistency of the substance of the germ is more nearly that of the yolk, and the surface curvature of the early blastomeres corresponds with that of the egg. In general cleavage planes are deepest in the region of the animal pole, becoming more and more superficial as they pass around the egg to its lowermost point: they agree in general direction with those of Lepidosteus but are irregular in their mode of occurrence from the second plane onward. In pigmentation the eggs of Acipenser present the strongest contrast to those of the Gar-pike. 1 As noted by Salensky and others. The stages of late segmentation may thus be contrasted. In Lepidosteus the division of the blastomeres results in a cap of cells of irregular sizes: this appears as a distinct prominence of the egg surface: below it a smooth surfaced periblast-like layer contributes at irregular points to the growth of the blastoderm,--a condition maintaining till the time of gastrulation. The cell cap of Acipenser is far more closely continuous with the yolk; cells large and irregular in size are readily distinguished in an intermediate zone between blastoderm and yolk: of this zone the number of tiers of cells agrees in a general way with that of the merocytes in corresponding stages of Lepidosteus. The general differences in segmentation appear due to either a greater or decreased amount of the egg's reserve of yolk material. But, everything considered, it seems to the present writer more probable that the mode of...
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Reseña del editor
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. 1894 edition. Excerpt: ... blastomeres almost conventional outlines; it is only after the fourth cleavage that variations are observed. In Acipenser, on the other hand, segmentation is holoblastic, although the furrows traversing the yolk region are of an exceedingly superficial character.1 The consistency of the substance of the germ is more nearly that of the yolk, and the surface curvature of the early blastomeres corresponds with that of the egg. In general cleavage planes are deepest in the region of the animal pole, becoming more and more superficial as they pass around the egg to its lowermost point: they agree in general direction with those of Lepidosteus but are irregular in their mode of occurrence from the second plane onward. In pigmentation the eggs of Acipenser present the strongest contrast to those of the Gar-pike. 1 As noted by Salensky and others. The stages of late segmentation may thus be contrasted. In Lepidosteus the division of the blastomeres results in a cap of cells of irregular sizes: this appears as a distinct prominence of the egg surface: below it a smooth surfaced periblast-like layer contributes at irregular points to the growth of the blastoderm,--a condition maintaining till the time of gastrulation. The cell cap of Acipenser is far more closely continuous with the yolk; cells large and irregular in size are readily distinguished in an intermediate zone between blastoderm and yolk: of this zone the number of tiers of cells agrees in a general way with that of the merocytes in corresponding stages of Lepidosteus. The general differences in segmentation appear due to either a greater or decreased amount of the egg's reserve of yolk material. But, everything considered, it seems to the present writer more probable that the mode of...
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