464 RADIATA. 



In Asterias and Ursinus, called EcHiNODKttMEs by Brugierc on 

 account of their spines, we find a distinct intestine floating in a hjrge 

 cavity, and accompanied by other organs, for generation, respiration, 

 and a partial circulation. The Holcthuriae were necessarily united to 

 them on account of the analogy of their internal organisation, which is 

 perhaps still more complex, although they have no moveable spines on 

 the skin. 



The ENTOZOA or Intestinal Worms, which form the second class, 

 have no very evident vessels in which a distinct circulation is carried 

 on, or separate organs of respiration. Their body is usually elongated 

 or depressed, and their organs arranged longitudinally. The difference 

 in their system of digestion will hereafter probably cause them to be 

 divided into two classes, a circumstance already indicated by our 

 establishing two orders. In some we find an alimentary canal sus- 

 pended in a true abdominal cavity, which is wanting in the others. 



The third class comprises the ACALEPHA or Sea Nettles. They 

 have neither true circulating vessels nor organs of respiration. Their 

 form is usually circular and radiating, and their mouth is almost always 

 their anus. They only differ from Polypi in the greater development 

 of the tissue of their organs. The Acalepha Hydrostatica, which we 

 place at the end of this class, when better known, will perhaps form a 

 separate one ; as yet however we can only conjecture the functions of 

 their singular organs. 



The POLYPI, which compose the fourth class, are those little gelati- 

 nous animals whose mouth surrounded with tentacula leads to a stomach 

 sometimes simple and sometimes followed by intestines in the form of 

 vessels. To this class belong those innumerable compound animals 

 with a fixed and solid stem which were considered as marine plants. 



The Thethyiae and Sponges are usually placed at the end of this 

 class, although Polypi have not yet been discovered in them. 



The INFUSORIA, or the fifth and last class of the Zoophyta, are those 

 minute beings whose existence we have only discovered by means of the 

 microscope, and which swarm in stagnant waters. Most of them have 

 merely a gelatinous body destitute of viscera, although we commence 

 the series with more compound species possessed of visible organs of 

 locomotion and a stomach : these also may hereafter constitute a sepa- 

 rate class. 



