1864.] DR. DAWSON ON CLASSIFICATION OF ANIMALS. 253 



form, they may be termed doubly symmetrical animals ; with 

 reference to their nervous system, Myelencephalous. 



2. Articulata,^ including Arachnida, or spiders and 

 scorpions; Insects; Crustaceans, and Worms. These animals 

 are bilateral and symmetrical, have an external annulose skeleton, 

 a nervous system, consisting of a ring and ganglion around the 

 gullet, connected with a double abdominal nerve-cord. They are 

 otherwise named Annulosa^ longitudinal animals, or Homogan- 

 gliata. 



3. MoLLUSCA, including Cuttle-fish and their allies; Gaster- 

 opods or univalve shell-fishes and their allies ; Lamellibranchiates 

 or bivalve shell-fishes, &c. ; Brachiopods and their allies. They 

 are bilateral but not always symmetrical, have no skeleton, and 

 an oesophageal nervous ring with nerve-fibres and ganglia not 

 symmetrically disposed. They are otherwise named massive 

 animals, or Heterogangllata. 



4. Eadiata, including Sea-urchins and starfishes ; Sea-nettles 

 and hydras ; Polyps and coral-animals ; and Sponges and their 

 allies. These have the parts arranged radially around a central 

 axis, and the nerve-system when discernible consisting of a central 

 ring with radiating fibres. They may be otherwise named peripheric 

 animal-, or JSfematoneura. 



This fourfold division includes the whole animal kino-dom, 

 and is the only rational one which can be based on type or plan of 

 structure. Since the time of Cuvier, though modifications in 

 detail have become necessary, it has been strengthened by the 

 progress of discovery ; and more especially Yon Baer has shown 

 that the study of embryology establishes Cuvier's branches, by 

 showing that in their development, animals pass through a series 

 of forms belonging to their own branch and to that only. 



The attempts which have been made to introduce additional 

 branches or provinces, I regard as retrograde steps. Such for 

 example is the province Coelenterata of Leuckart, including the 

 Polyps and the Acalephs, both of them good classes, but not 

 together constituting a group equivalent to a Province ; the 

 Province Protozoa of Siebold, which to resume our architec- 

 tural figure, includes merely the huts and cabins which it is difficult 

 to refer to any style of architecture, but which do not, on that 



* I prefer this term to " Anaulosa," as being Cuvier's original name — 

 a fact which should overrule merely verbal objections. 



