He defined them as possessing radial instead of bilateral symmetry, and as apparently destitute of nervous system and sense organs, as having the circulatory system rudimentary or absent, and the respiratory organs on or coextensive with the surface of the body; he included under this title and definition five classes, - Echinodermata, Acalepha, Entozoa, Polypi and Infusoria.
Milne-Edwards removed the Polyzoa; the group was soon further thinned by the exclusion of the Protozoa on the one hand and the Entozoa on the other; while in 1848 Leuckart and Frey clearly distinguished the Coelenterata from the Echinodermata as a separate sub-kingdom, thus condemning the usage by which the term still continued to be applied to these two groups at least.
These attempts, however, to perpetuate the usage were finally discredited by Huxley's important Lectures on Comparative Anatomy (1864), in which the term was finally abolished, and the "radiate mob" finally distributed among the Echinodermata, Polyzoa, Vermes (Platyhelminthes), Coelenterata and Protozoa.
Westward of and above these strata, the Middle and Upper Jurassic formations are found (Lias, Lower Oolite, Oxfordian, &c.), with well-marked and numerous fossils (Ammonites, Nerinaea, Natica, Astarte, Rhynchonella, Echinodermata, &c.); then the Cretaceous rocks, both these and the Jurassic series being largely developed, the Cretaceous fossils including Nautilus, Belemnites, Ostrea, Gryphaea, &c., and some very large Ammonites (Pachydiscus).
