Hidden in footnote 5 is a significant fact about the two-headed planaria (flatworms) that produce two-headed offspring: they reproduce not by laying eggs, but b

Hidden in footnote 5 is a significant fact about the two-headed planaria (flatworms) that produce two-headed offspring: they reproduce not by laying eggs, but by fission. In other words, this physiological trait is not passed through the genes (if it were, that would be a rather astounding Lamarckian fact). Planaria in general reproduce sexually (with eggs and sperm) and asexually (by splitting).