388 ANJMALU RADIATA. 



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

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

 freqviently, 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 correponding to the organs of respira- 

 tion, and the other merely serving to inflate the organs which supply 

 the want of feet. The latter is only distinctly visible in Ursinus 

 and Asterias. Through the gelatinous substance of the Medusae we 

 can see more or less complicated canals arising from the intestinal 

 cavity; all this precludes the possibility of a general circulation, and 

 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 anus, with a distinct intestinal 

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

 serving both for a mouth and anus. In the greater number there is 

 merely a cavity excavated in the substance of the body, which some- 

 times 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 her- 

 maphroditical and oviparous ; some have no genital organs, and 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 apparent 

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

 voluntary motion, mostly feed on matters which they have swallowed 

 or sucked, and digest them in an internal cavity, they are certainly 

 animals in every point of view. 



The greater or less degree of complication in Zoophytes has occa- 

 sioned their division into classes ; but as all the parts of their orga- 

 nization are not yet well known, those sections cannot be charac- 

 terized with as much precision as those of the preceding divisions. 



In Asterias and Ursinus, called Echin-odxrmes by Brugiere on ac- 



