CHAPTER XXI. 

 GENERAL CHARACTERS OF RADIATA. 



986. THE Radiated subdivision of the Animal Kingdom may 

 be regarded as, on the whole, a very natural group. It includes 

 all those animals, in which there is a regular disposition of similar 

 parts around a common centre, as in the Star-fish (Fig. 606), or 

 Sea- Anemone (Fig. 617)- In the most characteristic forms of 

 this group, these parts are but repetitions of each other ; and 

 one or more of them may be removed without injury to the 

 functions of the rest. It is by no means uncommon to meet 

 with Star-fish, which, by some accident, have been deprived of 

 a ray, and yet appear to have suffered but little inconvenience 

 from the loss. In most of the Radiata, the parts so lost are 

 replaced by a new growth ; and not unfrequently it would appear 

 that these parts may themselves reproduce the whole structure. 

 Here, then, is an important character, which evidently displays 

 an affinity with the Vegetable Kingdom. In Plants we observe 

 that the whole structure is made up of an assemblage of similar 

 parts the leaf-buds which may almost be regarded as distinct 

 individuals ; for though, whilst associated, they contribute to 

 form a structure which is common to all, and share alike in per- 

 forming the functions of that structure, yet they may be separated 

 from it and from each other without the loss of their vitality, if 

 placed in circumstances favourable to their growth under this 

 new condition. We shall presently observe that, in the POLY- 

 PIFERA, compound structures are produced by the association of 

 individuals, which have very nearly the same relation to each 

 other, and to the whole mass, as exists amongst the buds of a 

 tree, and between these and the woody trunk and branches. 



987. But it is not only in this repetition of similar parts, that 

 we may trace an affinity between the RADIATA and Plants. The 



