Journal of experimental zoology . king of the germinal vesicle theectoplasm covers the upper two-thirds of the egg; as soon as thegerminal vesicle breaks down, it flows toward the vegetative pole,and, even before the first maturation spindle has become fixedat the animal pole, it has completely overflowed it (Figs. 2 and 4),thus covering up the exposed endoplasm. The membrane accom-panies the ectoplasm and so covers the entire egg. This move-ment of the ectoplasm is clearly visible in the living egg as a seriesof waves of the transparent external pellicle; but, owing to thedifliculty of orient
Journal of experimental zoology . king of the germinal vesicle theectoplasm covers the upper two-thirds of the egg; as soon as thegerminal vesicle breaks down, it flows toward the vegetative pole,and, even before the first maturation spindle has become fixedat the animal pole, it has completely overflowed it (Figs. 2 and 4),thus covering up the exposed endoplasm. The membrane accom-panies the ectoplasm and so covers the entire egg. This move-ment of the ectoplasm is clearly visible in the living egg as a seriesof waves of the transparent external pellicle; but, owing to thedifliculty of orienting the living egg in this stage, I have not beenable to follow the course of the weaves satisfactorily. The sec-tions, however, that enable one to trace the overflow of the vege- Elementary Phenomena of Ej?7bryonic Developjnent 169 tative pole, leave no doubt that they are associated with thisprocess. At the end of the polarization period the ectoplasm around thecenter of the vegetative hemisphere is as thick as anyvs^here Fig. 2. Axial section through a primary ovocyte, killed about ten minutes after coming intosea-water, and three minutes after fertilization. The ectoplasm has already flowed to thevegetative pole, leaving an exposed area of endoplasm at the animal pole. Part of the a endoplasmhas likewise flowed to the vegetative pole. The germinal vesicle has broken down and the maturationspindle is in process of formation between the two primary asters. The residual substance of the ger-minal vesicle is clearlv seen. The chromosomes do not fall in the plane of the section. Letters sameas in Fig. i. The original opening in the ectoplasm at the animal pole hasbecome enlarged, and the outer end of the maturation spindle isfixed here (Figs. 2-5). Endoplasm.—The endoplasm consists of three distinct partsas already described, {a) the uppermost part laden with large 170 Frank R. Lillie spherules; (b) the non-spherular part overlying the germinalvesicle; (c) the vacuolate
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1904
