388 ANIMALIA RADIATA, 
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 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 Medusze 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 Ecuinopermes by Brugiere on ac- 
. 
