 Gurney's two great study objects were the Copepoda and the larvae of Decapoda, and his greatest works were the three-volume monograph "British Freshwater Copepoda", published by the Ray Society in 1931–1933, and his "Larvae of Decapod Crustacea" published by the Ray Society in 1942.Perhaps through the influence of Garstang, Gurney rejected Ernst Haeckel's biogenetic law (that "ontogeny recapitulates phylogeny"), preferring Garstang's concept of paedomorphosis as an explanation for the similarities between copepods and decapod larvae.Gurney was, however, very tentative in his speculations.