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| | The Metazoa |
 | | The ovum, after impregnation, divides into cleavage masses, or blastomeres, giving rise to a Morula, in the midst of which arises a cavity, the blastocoele (cleavage cavity, "Furchungshohle" of the Germans), which may be larger or smaller, filled only with fluid, or occupied by food yelk. |
 | | When it is largest, the blastomeres, disposed in a single later, form a spheroidal vesicle, enclosing a correspondingly shaped blastocoele. |
 | | When it is reduced to a minimum, the Morula is an almost solid aggregation of blastomeres, which may be nearly equal in size, or some may be much larger than others, in consequence of having undergone less rapid division. |
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