498 ANIMALIA RADIATA. 



supply the want of feet. In the great number of Zoophytes it is 

 easily proved that there are no vessels whatever. 



In some genera, such as Holothuria, Ursinus, and in several of 

 the Entozoa, we observe a mouth and a distinct intestinal canal. 

 Others have an intestinal sac, but with a single opening. In the 

 greater number there is merely a cavity excavated in the substance 

 of the body which sometimes opens by several suckers; and finally 

 there are some in which there is no mouth visible, and which can 

 only be nourished by porous absorption. 



The sexes of several of the Entozoa or Intestinal Worms can be 

 distinguished. The greater number of the other Radiata are ovi- 

 parous; some are reproduced by buds or division. 



The compound animals, of which we have already seen some ex- 

 amples in the last of the Mollusca, are greatly multiplied in certain 

 orders of the Radiata, and their aggregation produces trunks and 

 expansions forming all sorts of figures. It is to this circumstance, 

 together with the simple nature of the organization in most of the 

 species, and the radiating disposition of their organs, which reminds 

 us of the petals of flowers, that they owe their name of Zoophytes 

 or Animal-plants, by which we merely mean to express this appa- 

 rent affinity, for as Zoophytes enjoy the sense of touch and the power 

 of voluntary motion, mostly feed on matters which they have swal- 

 lowed or sucked, and digest them in an internal cavity, they are cer- 

 tainly animals in every point of view. 



In Asterias and Ursinus, called Echinodermes by Brugiere on 

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

 cavity, and accompanied by other organs, for respiration, &c., and 

 a partial circulation. 



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

 have no very evident vessels in which a distinct circulation is car- 

 ried on, nor separate organs of respiration. Their body is usually 

 elongated or depressed, and their organs arranged longitudinally. 



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 al- 

 most always their only aperture. They only differ from Polypi in 

 the greater development of the tissue of their organs. The Aca- 

 lepha Hydrostatica, which we place at the end of this class, when 



