. The elements of experimental embryology. Embryology, Experimental; Embryology. Fig. 48 Diagram to show the influence of the primary axial gradient in fusion-experi- ments with sea-urchin eggs. Left, single egg and resultant pluteus. Centre, two eggs united with their axes parallel produce a single pluteus. Right, two eggs united with their axes at an angle produce double monsters. (From Przibram, Handb. norm, andpathol. Physiol, xiv, 1925, fig. 411, p. 1099.) A good example of this is found in Ctenophores. Here the adult has eight swimming plates or costae. But although in these forms the fi
. The elements of experimental embryology. Embryology, Experimental; Embryology. Fig. 48 Diagram to show the influence of the primary axial gradient in fusion-experi- ments with sea-urchin eggs. Left, single egg and resultant pluteus. Centre, two eggs united with their axes parallel produce a single pluteus. Right, two eggs united with their axes at an angle produce double monsters. (From Przibram, Handb. norm, andpathol. Physiol, xiv, 1925, fig. 411, p. 1099.) A good example of this is found in Ctenophores. Here the adult has eight swimming plates or costae. But although in these forms the first two cleavage divisions are meridional, larvae developed from 1/2 blastomeres have only four costae: i/8 and 1/4 blasto- meres give larvae with one and two costae respectively.^ In the un- cleaved tgg of Beroe, there is a complete and uniform peripheral layer of a clear substance which appears green by dark-field illu- mination. By an elaborate series of changes, due to streaming move- ments of the peripheral zone, and to alternation of more viscous and less viscous phases in the general cytoplasm, the end of cleavage sees this green substance lodged in the micromeres and forming their entire contents, while none of it remains in the macromeres. The micromeres give rise to the ectoderm, including the costae,- and contain some materials, precociously chemo-differentiated in the green substance, needed for costa-formation (figs. 49, 50). At the beginning of each cleavage division during the early 1 Fischel, 1898. 2 spek, Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Huxley, Julian, 1887-1975; De Beer, Gavin, Sir, 1899-1972. New York [Hafner Pub. Co. ]
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