GENERAL CHARACTERS OF RADIATA. 447 



The resemblance is manifested, also, in the regular disposition of 

 these parts around a common centre, which may be termed cir- 

 cular symmetry. The tendency to this kind of symmetry exists 

 throughout the Vegetable Kingdom ; being most obvious in the 

 arrangement of the parts of the flower (VEGET. PHYSIOL. 463). 

 That the Radiata should preserve the mode of development, 

 which is so remarkably characteristic of the Vegetable Kingdom, 

 is not surprising, when we reflect upon the very small propor- 

 tion which their animal functions bear to those of organic life. 

 None of them possess any high degree of sensibility ; and whilst 

 many of them are fixed like plants during a part or the whole 

 of their existence, none possess any very active powers of loco- 

 motion. 



1082. Although the radiated form may be observed in cer- 

 tain members of every class which has an undoubted claim to 

 admission into this group, it by no means follows that it should 

 exist in each individual of those classes. Like every other 

 natural character, it is subject to modifications. The species 

 which present it in the most remarkable degree may be regarded 

 as the typical forms of their respective groups ; whilst others, 

 in which it is less evident or altogether absent, serve as con- 

 necting links with those divisions of the Animal Kingdom which 

 are formed upon a different plan. Thus, among the POLYPIFERA, 

 the Sea-Anemone, and many of the associated animals resem- 

 bling it, have a most regular arrangement of similar parts, both 

 externally and internally, around a common centre. In other 

 nearly allied forms, however, we have more difficulty in recog- 

 nising the radiate arrangement ; and the title of many of these 

 to a place in this subdivision rests upon other grounds, which 

 will be hereafter referred to. In like manner we have, in the 

 Star-fish, a perfectly symmetrical disposition of all the organs of 

 the body. The stomach, situated in the centre, sends. a prolon- 

 gation into every arm ; the nervous system has a central ring, 

 and sends equal branches in every direction ; the locomotive 

 organs are the same in each division of the body ; and at the 

 extremity of each ray (in the species possessed of visual organs) an 

 eye of equal size exists. But in the Echinus (Fig. 706), with 



