CLASSIFICATION. 3 



skull and a backbone or vertebral column ; and this division 

 is so convenient and so obvious that it is still retained. 

 But Baron Cuvier pointed out, that great and important 

 differences exist among the invertebrate animals, or those 

 which are destitute of a skull and vertebral column — dif- 

 ferences so great as to justify a further subdivision; and 

 that, according to the modifications of the nervous system, the 

 entire animal kingdom might be divided into four primary 

 groups, — one of them consisting of the vertebrated animals, 

 and three of those which arc invertebrated. Adopting these 

 views, we follow the illustrious Cuvier in dividing the whole 

 animal kingdom into four great groups, or sub- kingdoms; 

 namely, — 



L Vertebrated animals, or Vertehrata; 



[iNVERTEBRATA.] 



II. Soft-bodied animals, or Mollusca; 



III. Articulated animals, or Articulaia; 



IV. Radiated animals, or Radiata. 



To begin with those at the foot of the scale and gradually 

 ascend, is the best mode of preparing to enter with advantage 

 on the consideration of the higher ranks of organized beings. 

 Our attention should, therefore, be directed, in the first place, 

 to the Eadiated animals. 



RADIATED ANIMALS. 



" Lord, how manifold are tliy works ! in wisdoni hast thou made 

 them all: the earth is full of thy riches: so is this great and wide sea, 

 wherein are things creeping innumerable, both small and great beasts."—!. 

 FsAuus. 



If we pick up a common star-fish, which has been left upon 

 the beach by the retiring tide, we notice that the limbs or 

 aims of the animal are like radii, diverging from a common 

 centre, or like rays surrounding a central disc. From this 

 circumstance it is termed a "rayed" or "radiated" animal. 



In other species belonging to the same great class, the 

 radiated structure is not at first sight so obvious. It will, 

 however, be easily detected in the sea-urchin (echinus), although 



