66 



RADIATED TYPE OP 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 

 i :o. 26SuA ANB- P lace to tne lateral symmetry, are aberrant 

 MONK. forms, that conduct us towards other groups. 



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



