. The elements of experimental embryology. Embryology, Experimental; Embryology. i8 CLEAVAGE AND DIFFERENTIATION and the prelocalisation of organ-forming substances appeared to be of considerable theoretical importance. From the point of view here adopted, the absence of prelocalisation in such cases is seen to be a frequent (though not universal) consequence of precocious >»^'-'^P C. Oy-i- Fig. 56 Localisation of organ-forming substances in Ascidians. Views of eggs of Styela. Yellow cytoplasm containing mitochondria {yp) small circles. Yolk {Gy) stippled. Clear cytoplasm {cp) white. A, Bef
. The elements of experimental embryology. Embryology, Experimental; Embryology. i8 CLEAVAGE AND DIFFERENTIATION and the prelocalisation of organ-forming substances appeared to be of considerable theoretical importance. From the point of view here adopted, the absence of prelocalisation in such cases is seen to be a frequent (though not universal) consequence of precocious >»^'-'^P C. Oy-i- Fig. 56 Localisation of organ-forming substances in Ascidians. Views of eggs of Styela. Yellow cytoplasm containing mitochondria {yp) small circles. Yolk {Gy) stippled. Clear cytoplasm {cp) white. A, Before fertilisation, showing germinal vesicle {GV), yellow cytoplasm evenly distributed over the surface. B, Imme- diately after fertilisation, showing clear region {kp) derived from germinal vesicle at animal pole, yellow cytoplasm streaming down to vegetative pole. C, The yellow cytoplasm forms a cap at the vegetative pole {yz) containing the male pronucleus. The clear cytoplasm forms a layer just above it. D, Left side view of egg just before first cleavage, showing yellow crescent {yc) and clear crescent {cp) posterior, and grey crescent (Gc) anterior. (From Conklin, Chap. IX of Cowdry, General Cytology, Chicago, 1924.) chemo-differentiation. When chemo-differentiation occurs prior to fertilisation, the differentiated substances thus produced are able to shift their relative positions, either in the uncleaved tgg, or as a result of manoeuvres effected during cleavage. If, on the other hand,. 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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Keywords: ., bookcentury1900, bookcollectionbiodiversi, booksubjectembryology
