RADIATED TYPE OF STRUCTURE. 



star-shaped or a globular form. This we see in the Star-fish 

 (Fig. 25), the Echinus or Sea-Urchin, most of the Jelly-fish, 



FIG. 25. STAR-FISH. 



and in nearly all the Polypes, when we look at them separately 

 (Fig. 26). Sometimes this arrangement is perfectly symmetri- 

 cal ; that is, every division of the body exactly resembles the 

 others in form and size ; but in other instances we see that the 

 parts of the structure have a tendency to arrange themselves 

 equally on the two sides of a central line, so as 

 to approach that li-lateral symmetry, or equa- 

 lity of the two halves of the body, which is 

 characteristic of the Articulata and Verte- 

 brata. Those in which the radial or circular 

 symmetry is perfect, are to be regarded as the 

 typical Radiata ; whilst those in which it gives 

 place to the lateral symmetry, are aberrant 

 forms, that conduct us towards other groups. 

 The resemblance of the parts of the body, in Radiated animals, 



FIG. 26. SEA ANE- 

 MONK. 



