44 CLASSIFICATION AND CREATION. 



flat roof and the colonnade are typical of all 

 Grecian temples, whether built of marble or 

 granite or wood, whether Doric or Ionic or 

 Corinthian, whether simple and massive or light 

 and ornamented ; and, in like manner, the steep 

 roof and pointed arch are the typical characters 

 of all Gothic cathedrals, whatever be the material 

 or the details. The architectural conception re- 

 mains the same in all its essential elements, how- 

 ever the more superficial features vary. Such 

 relations as these edifices bear to the architec- 

 tural idea that includes them all, do classes bear 

 to the primary divisions or branches of the Ani- 

 mal Kingdom. 



The three classes of Radiates, beginning with 

 the lowest, and naming them in their relative 

 order, are Polyps or Sea-anemones and corals, 

 Acalephs or Jelly-Fishes, and Echinoderms or 

 Star-Fishes, Sea-Urchins and the like. In the 

 Polyps the plan is executed in the simplest 

 manner ; the body consists of a sac, the sides 

 of which are folded inward, at regular intervals, 

 from top to bottom, so as to divide it by vertical 

 radiating partitions, converging from the periph- 

 ery toward the centre. These folds do not meet 

 in the centre, but leave an open space, which is 

 the main cavity of the body. This open space, 

 however, occupies only the lower part of the 

 body; for in the upper there is a second sac 



