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FOURTH GREAT DIVISION OF THE ANIMAL 

 KINGDOM. 



ANIMALIA RADIATA. 



The Radiated Animals, or Zoophytes, as they are termed, 

 include a number of beings whose organization, always evidently 

 more simple than that of the three preceding divisions, also presents 

 a greater variety of degrees than is observed in either of them, and 

 seems to agree in but one point, viz. their parts are arranged round 

 an axis and on one or several radii, or on one or several lines ex- 

 tending from one pole to the other. Even the Entozoa or Intestinal 

 Worms have at least two tendinous lines, or two nervous threads 

 proceeding from a collar round the mouth, and several of them have 

 four suckers situated round a probosciform elevation. In a word, 

 notwithstanding some irregularities, and some very few exceptions — 

 those of the Planaria and most of the Infusoria — traces of the radi- 

 ating form are always to be found, which are strongly marked in the 

 greater number, and particularly in Asterias, Echinus, the Acale- 

 pha, and the innumerable host of the Polypi. 



The nervous system is never very evident, and when traces of it 

 have been apparently visible, it was also arranged in radii; most 

 frequently, however, there is no appearance of it whatever. 



There is never any true circulating system. The Holothuria are 

 provided with a double vascular apparatus, one portion of it being 

 attached to the intestines and corresponding to the organs of respi- 

 ration, and the other merely serving to inflate the organs which 

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