FOURTH SUB-KINGDOM 



RADIATES. (Lat. radius, a ray.) 



THIS includes animals so named from the arrangement of the 

 parts round an axis somewhat as in plants ; hence they were 

 called by Cuvier, ZOOPHYTES, Plant-like animals. These intro 

 duce us to the 



NINTH BRANCH OF ZOOLOGY. 



ACTINOLOGY, (Gr. uxTlv, aktin, a ray ; koy6g, logos, a discourse. 



RAY-LIKE ANIMALS. 



The terms which are here employed are not, by any means, 

 equally applicable to all the beings included in this last sub-divis 

 ion of the Animal Kingdom. While in some of them the radiated 

 arrangement of the parts is very easily seen, in others it can 

 be traced only by a close microscopic examination. Agassiz says 

 it can be perceived in all with &quot;sufficient observation.&quot; Such 

 are the differences of form and in the degree of organization 

 among the Radiates, that instead of undertaking to present addi 

 tional characters, describing them as a whole, we shall at once 

 proceed to consider the four classes into which they are divided. 



I. ECHINODERMS, (Gr. e/ZVo?, echinos, a sea-urchin ; 

 derma, skin.) 



These are all marine, and characterized by having a well or 

 ganized skin, under which or attached to which are often found 

 plates of solid matter, forming a kind of skeleton, and some 

 times joined together like the stones of a pavement. They 

 have a digestive and, vascular system. A circular nervous sys- 



