. Analysis of development. Embryology; Embryology. Amphibians 231 animal pole has moved. Obviously, we are dealing with a second rotation-phenomenon ("rotation of symmetrization," Ancel and Vintemberger, '48). It has been generally assumed that this rotation involves the en- tire egg, leading to a redistribution of heavy and light materials and to a shift of the center of gravity. However, Ancel and Vin- temberger (since '32, see '48) have demon- strated for R. fusca, by means of electro- cautery marks, that only the egg surface is involved. The cortex glides over the heavy materials
. Analysis of development. Embryology; Embryology. Amphibians 231 animal pole has moved. Obviously, we are dealing with a second rotation-phenomenon ("rotation of symmetrization," Ancel and Vintemberger, '48). It has been generally assumed that this rotation involves the en- tire egg, leading to a redistribution of heavy and light materials and to a shift of the center of gravity. However, Ancel and Vin- temberger (since '32, see '48) have demon- strated for R. fusca, by means of electro- cautery marks, that only the egg surface is involved. The cortex glides over the heavy materials of the center, which later remain Interest in these problems has been revived more recently. Some authors contend that a bilateral symmetry pre-exists in all unfertilized am- phibian eggs and not only in those in which it is actually visible. The appearance of normal symmetry relations in eggs which have been activated by chemical agents or by electrical shock may be cited in support of this contention. Such an inner organiza- tion would originate in the ovary. Numerous investigations have shown that whatever intrinsic organization pre-exists,. a b Fig. 75. Diagram of the structure of an unfertilized frog's egg (a) before and (b) after rotation of sym- metrization (after Ancel and Vintemberger, '48, Fig. 35). a. Animal pigmented cytoplasm with small yolk granules; an, anu position of animal pole before and after rotation; b, central pigmented yolk area; c, vegetal unpigmented area with large yolk granules; m-n, m.\-n\, ventral margin of pigment before and after rotation. static except for a slight shift in the marginal plasma (Fig. 75), The origin of the gray crescent is not clearly understood. According to the above avithors, it originates in anurans in the fol- lowing way: on the future dorsal side, only the cortical plasma carrying pigment moves upward, but the more deeply located pig- ment is left behind. The latter is thus over- laid by a thin layer of unpigmented plasma,
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Keywords: ., bookcentury1900, bookpublisherphiladelphi, booksubjectembryology
