334 NATURAL HISTORY. 



order whose animals breathe by gills ? What is said of the Whorl 

 family ? What of the family called Buccinidae ? What is said of the 

 Cowry ? What is said of the third order of Gasteropods ? What are 

 the two groups of Acephalous Mollusks ? What are the shells of the 

 Conchiferous group ? What does it include ? In what way is the 

 shell formed ? How are the two valves united ? How moved ? 

 What is the anatomy of the Acephala ? What is said of the symme- 

 try of these animals ? What are the two sections of the Conchifera ? 

 What is said of the Oyster ? What of the Pearl Oysters ? What of 

 the Pectens ? What are among the Conchifera that have siphons ? 

 What is said of the Tridacna? What is said of the Cockles, the 

 Veneraceas, and the Pholadacese? What of the Teredo? What of 

 the Razor-shell ? What is said of the various ways in which the foot 

 is used by Mollusks ? What is said of the Ocean Snails ? What is 

 said of the Tunicata ? 



CHAPTER XXXIV. 



RADIATES. 



575. WE now come to the last sub-kingdom that of 

 the Radiates. The arrangement of structure here is, in 

 many respects, entirely different from that of the other 

 sub-kingdoms. There is a lateral symmetry of form in 

 the Vertebrates and the Articulates. While this is most- 

 ly abandoned in the Mollusks, in the Radiates it is ex- 

 changed for another symmetry of a wholly different char- 

 acter a symmetry of rays arranged circularly. It is 

 therefore akin to that of plants. Indeed, many of the 

 animals of this sub-kingdom were formerly supposed to 

 be plants, and are now, from the resemblance referred to, 

 called plant-animals. 



576. This resemblance may be very distinctly seen in 

 the Actiniae, or Sea Anemones, of which there are many 

 species. The structure of these is very singular. There 

 is a broad, flat, muscular base, of a circular shape, by 

 which the animal adheres firmly to a rock. From this 

 base rises a rounded body, on the top of which there is 

 an orifice, which is more or less open according to cir- 



