377 



FOURTH GREAT DIVISION. 

 RADIATA.* 



IN all the varied forms which have as yet fallen 

 under our notice, there has been an arrangement of 

 the external organs on each side of an imaginary line 

 running down the body, so that if the animal were 

 split in this line, the one portion should, externally, 

 exactly correspond to the other. But in the inferior 

 forms we now meet with, this arrangement no longer 

 exists ; there is no longer any definite part, of 

 which we may say, this is the fore, or this the hind 

 extremity ; this is the right, or this the left side. 

 Yet these creatures are not shapeless, nor devoid of 

 symmetry, but it is a symmetry of a peculiar charac- 

 ter. The organs are no longer disposed in a longitu- 

 dinal parallel series, but in a circular form, being 

 arranged round a centre. It is true, this radiation is 

 in a few cases scarcely observable without anatomical 

 examination, but it is the general character, and 

 commonly quite obvious. 



The creatures of this Division, going down to 

 the very bottom of the animated scale, where animal 

 life seems, indeed, to merge into vegetable, so gra- 

 * Radio, to diverge from a centre, as the spokes of a wheel. 



