INTRODUCTORY CHAPTER. 27 



the ninth and tenth of Lamarck's system of 

 animal nature, the Conchifera, or Bivalves, and 

 the Mollusca, or Univalves, being the eleventh 

 and twelfth. The two former will be described 

 (though the animals are not considered as pos- 

 sessing true shells) on account of specimens of 

 the tubes or coverings being frequently found 

 in collections of shells. Lamarck arranges his 

 system in a regular succession, beginning with 

 the inferior animals, and describing them in or- 

 der as they gradually increase in powers and 

 complicated formation. On this account the 

 Annulata and Cirrhipeda come first, the animals 

 forming those coverings being very inferior in 

 organization to those of the other classes. # 



* The information contained in this chapter is chiefly 

 derived from Dr. Roget's Bridgewater Treatise, Mr. 

 Gray's article in the Philosophical Transactions for 

 1833, and various articles in the Penny Cyclopaedia, &c. 



