834 NATUKAL HISTOKT. 



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

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

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

 the two groups of Acephalous MollusUs ? 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 Conc-hifera ? 

 What is said of the Oyster ? What of the Pearl Oystei-s ? What of 

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

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

 Venernceae, and the Pholadaceas? What of the Teredo ? What of 

 the Eazor-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 

 xaid of the Tunicata ? 



CHAPTER XXXIV. 



EADIATES. 



5^5. We now come to the last sub-kingdom — that of 

 the Radiates. The arrangement of structure here is, iii 

 many respects, entirely diiferent 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 symmetrj'' of rays arranged circularl}-. 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 Actinise, 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 

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



