In Aeginopsis a planula is formed by multipolar immigration.
As division proceeds, the filamentous nature of this cytoplasm becomes more prominent and the threads begin either to converge towards the poles of the nucleus, to form a bipolar spindle, or may converge towards, or radiate from, several different points, to form a multipolar spindle.
When the blastula is spherical and not set free, the germ-layer formation is always multipolar, either by immigration or by delamination, i.e.
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