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I told them about jellyfish life cycles—that jellies start off almost like a plant, clinging to the bottom of the sea, and how in that phase of life, they are a planula.

As another illustration I may take the Magosphæra planula, discovered by Haeckel on the coast of Norway.

The eggs are not always laid in the condition of the simple planula described above.

The Norwegian Magosphaera planula, swimming about by means of the lashes or cilia at its surface.

Some said that the original embryonic form of the metazoa was not the gastrula, but the "planula"—a double-walled vesicle with closed cavity and without mouth-aperture; the latter was supposed to pierce through gradually.