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In other gall-flies and in aphids we find that a sexual generation alternates with one or with many virgin generations.

The spore of a fern or a moss has only half the number of chromosomes that the cells of its producer have, yet it proceeds by asexual multiplication or ordinary cell-division to build up the gametophyte or sexual generation.

The phenomena of inheritance in the sexual generation of hybrids show this clearly.

V-VIII represents the sexual generation.

On the crab being devoured by the right species of Cephalopod, the merozoites doubtless give rise to the sexual generation again.