 As an example of this, Darwin cited in his 1859 book "On the Origin of Species" the shrimp-like larva of the barnacle, whose sessile adults looked nothing like other arthropods; Linnaeus and Cuvier had classified them as molluscs.Darwin also noted Alexander Kowalevsky's finding that the tunicate, too, was not a mollusc, but in its larval stage had a notochord and pharyngeal slits which developed from the same germ layers as the equivalent structures in vertebrates, and should therefore be grouped with them as chordates.19th century zoology thus converted embryology into an evolutionary science, connecting phylogeny with homologies between the germ layers of embryos.