PROGRESS OF ANIMAL MORPHOLOGY. 4:79 



so that the animal has a right and a left side. In the radiata the 

 similar members radiate from the axis in a circular manner, like the 

 petals of a regular flower. 



The whole value of such a classification cannot be understood.with- 

 out explaining its use in enabling us to give general descriptions, and 

 general laws of the animal functions of the classes which it includes ; 

 but in the present part of our work our business is to exhibit it as an 

 exemplification of the reduction of animals to laws of Symmetry. 

 The bipartite Symmetry of the form of vertebrate and articulate ani- 

 mals is obvious ; and the reduction of the various forms of such ani- 

 mals to a common type has been effected, by attention to their 

 anatomy, in a manner which has satisfied those who have best studied 

 the subject. The molluscs, especially those in which the head disap- 

 pears, as oysters, 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 sug- 

 gested, to the kind of Symmetry found in plants. Some naturalists 

 have doubted whether 9 these zoophytes are not referrible to two types 

 (acrita or polypes, and true radiata,} rather than to one. 



This fourfold division was introduced by Cuvier. 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 Phi- 

 losophique : in this, I mark the characters and the limits of molluscs, 

 insects, worms, echinoderms, and zoophytes. I distinguish 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 Memoir 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; and since that 

 time the division has been commonly accepted among naturalists. 



[2nd Ed.] [The question of the Classification of Animals is 

 discussed in the first of Prof. Owen's Lectures on the Invertebrate Ani- 



Brit. Asxoc. Rep. iv. 227. 1 R' yue A. 01. 



