304 NATURAL HISTORY. 
order whose animals breathe by gills? What is said of the Whorl 
family? What of the family called Buccinide ? 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 
Veneracez, and the Pholadacee? 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. 3 
576. This resemblance may be very distinctly seen in 
the Actiniz, or Sea Anemones, of which there are many 
species. The structure of theseis 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- 
