. Text-book of embryology. Embryology. 610 INVEETEBEATA Fig. 442.—The egg of Cynthia partita before and during fertilization. (After Conkliu.) [The yellow cytoplasm is indicated by dotting the dark-blue cytoplasm by dark shading.] A, egg before fertilization with large germinal vesicle. B, egg immediately after fertilization, showing the down-streaming of the yellow cytioplasm and the outflow of the contents of the germinal vesicle. C, egg a little later, showing the aggregation of the yellow cytoplasm to form the yellow crescent at the posterior side of the egg. , clear cytoplasm
. Text-book of embryology. Embryology. 610 INVEETEBEATA Fig. 442.—The egg of Cynthia partita before and during fertilization. (After Conkliu.) [The yellow cytoplasm is indicated by dotting the dark-blue cytoplasm by dark shading.] A, egg before fertilization with large germinal vesicle. B, egg immediately after fertilization, showing the down-streaming of the yellow cytioplasm and the outflow of the contents of the germinal vesicle. C, egg a little later, showing the aggregation of the yellow cytoplasm to form the yellow crescent at the posterior side of the egg. , clear cytoplasm which will give rise to ectoderm; , egg - membrane ; , germinal vesicle; , test cells ; ;r^ yellow crescent. acid. Such material eau be stained with haematoxylin followed by eosin dissolved in oil of cloves, on the slide. Conklin commenced his study of the development with the ovarian egg. In the young oocyte there is no yolk, and the nucleus occupies a nearly central position in the egg. On the one side of the nucleus is a rounded mass which stains deeply with eosin. This Conklin considers to be the " attraction sphere," which functioned in the cell division which gave rise to the oocyte; it now functions as yolk-nucleus, the deposition of yolk-granules takes place round it as a centre. A layer of peripheral cytoplasm remains tree from yolk; in tlais, however, yellow pigment granules are deposited. The yolk spherules are of a slaty-grey colour. There is an enormous vesicular nucleus (germinal vesicle), with a large nucleolus, and near the nuclear membrane a few chromatin granules. As the oocyte grows it is surrounded by the so-called test cells. These are simply follicle cells or rudimentary ova; round the nucleus of each there is the same collection of yellow granules as are found in the peripheral layer of the ovum. These " test cells " become actually embedded in the peripheral layer of the oocyte whilst it is growing, but when it
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