494 HISTORY OF PHYSIOLOGY. 



or those which are rolled into a spiral, as snails, 

 have a less obvious symmetry, but here also we can 

 apply certain general types. And the symmetry of 

 the radiated zoophytes is of a nature quite different 

 from all the rest, and approaching, as we have 

 suggested, to the kind of symmetry found in plants. 

 Some naturalists have doubted whether 9 these zoo- 

 phytes are not referrible to two types (acrita or 

 polypes, and true radiata), rather than to one. 



This fourfold division was introduced by Cu- 

 vier 10 . Before him, naturalists followed Linnaeus, 

 and divided non-vertebrate animals into two classes, 

 insects and worms. "I began," says Cuvier, "to 

 attack this view of the subject, and offered another 

 division, in a Memoir read at the Society of Natural 

 History of Paris, the 21st of Floreal, in the year III. 

 of the Republic, (May 10, 1795,) printed in the 

 Decade Philosophique : in this, I mark the charac- 

 ters and the limits of molluscs, insects, worms, echi- 

 noderms, and zoophytes. I distinguished the red- 

 blooded worms or annelides, in a Memoir read to 

 the Institute, the llth Nivose, year X. (December 

 31, 1801). I afterwards distributed these different 

 classes into three branches, each co-ordinate to the 

 branch formed by the vertebrate animals, in a Me- 

 moir read to the Institute in July, 1812, printed in 

 the Annales du Museum d'Histoire Naturelle, torn. 

 xix." His great systematic work, the Regne Animal, 

 founded on this distribution, was published in 1817; 



9 Brit. Assoc. Rep. iv. 227. 10 Regne An. 61. 



