ANIMALIA RADIATA. 389 



count of their spines, we find a distinct intestine floating in a large 

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

 and a partial circulation. The Holothoriae were necessarily united 

 to them on account of the analogy of their internal organization, 

 which is perhaps still more complex, although they have no movable 

 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, nor separate organs of respiration. Their body is usually elon- 

 gated 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 

 suspended in a true abdominal cavity, Avhich 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 al- 

 ways their anus. They only differ from Polypi in the greater deve- 

 lopment of the tissue of their organs. The Acalepha Hydrostatica, 

 which we place at the end of this class, when better known, will per- 

 haps form a separate one ; as yet however we only conjecture the 

 functions of their singular organs. 



The Polypi, which compose the fourth class, are those little gela- 

 tinous 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 com- 

 pound animals with a fixed and solid stem, which were considered as 

 marine plants. 



The Thethyias 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 com- 

 mence the series with more compound species possessed of visible 

 organs of locomotion and a stomach : these also may hereafter con- 

 stitute a separate class. 



