Owing to such adaptations the similarity of the larvae of allied animals is sometimes greatly obscured; especially when there is a division of labour during the different stages of development, as when the same larva has during one stage to search for food, and during another stage has to search for a place of attachment.

Cases can even be given of the larvae of allied species, or groups of species, differing more from each other than do the adults.

In most cases, however, the larvae, though active, still obey, more or less closely, the law of common embryonic resemblance.