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Show A.NIMALIA RADIATA. 326 . 1 . d twithstanding some trregu art-form elevation. In a wor ' no t' ns--those of the Planaria few excep to ties, and some very s of the radiating form are h I f ria-trace and most of t e n uso ich are strongly marked in the greater always to be foun~, wh . A terias, Echinus, the Acalepha, number, and parttcularly In s p 1 . . bl host of the o YP1• and the Innumera e . ery evident and when traces tern 1s never v ' . The nervous sys 1 . 'ble it was also arranged m b Parent y VISI ' . of it have een ap 1 . there is no appearance of It radii ; most frequently' lowev er, whatever.. any true c.u c ulating system. The Holo- There IS neve~ , . h double vascular apparatus, one . ovtded wtt a d thurta are pr h d to the intestines and correspon · porti·o n of 1' t being attac e · • t' and the other merely servmg h s of resptra 10n, ing tot e organ h' h supply the want of feet. The to inflate the or?a~s ~ ICvisible in Ursinus and Asterias. latter is only distmct Y b t e of the Medusre we can see h 1 tinous su s anc . Through t e ge a . d ls arising from the intestmal 1 comphcate cana . more or ess d h ssibility of a general ctrcula- . • 11 this preclu es t e P0 • • • d cav1ty , a b f Zoophytes 1t IS eastly prove tion and in the great num er o ' no vessels whatever. . that there are h H 1 thuria Ursinus, and In several In some genera, sue as o o th a'nd anus with a distinct observe a mou ' . of the Entozoa, we h an I'ntestinal sac, but wtth a . · 1 1 Others ave mtestma cana . . b h ~ mouth and anus. In the . . serVIng ot lOr a . h smgle opemng . ly a cavity excavated ID t e b there IS mere 1 greater num er which sometimes opens by se:era substance of the body me 1 • n whreh there IS no d fi lly there are so suckers; an na . h ly be nourished by porous mouth visible, and whic can on abs6rption. . 1 f the Entozoa or Intestinal Worms The sexes of sev era o b of the other Ra- . . · h d The greater num er can be distmguishe d. 't' 1 and oviparous; some have no ge· d. t are hermap ro 1 ICa . . . .I a a d are repro d uce d by buds or d1 vtston. mtal organs, an . f which we have already seen The compou~d amma1s~fothe Mollusca, are greatly mu~tisome examples tn the last h R d' t and their aggregation plied in certain orders of t e a ta a, ANIMALIA RADIATA. 327 produces trunks and expansions forming all sorts of :figures. It is to this circumstance, togethel' 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 Zooph:ytes or .llnimal-plants, by which we merely mean to express this apparent affinity, for as Zoophytes enjoy the sense of touch and the power of vol'untary 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 o£. view. The grea~er or less degree of com plication in Zoophytes has occasioned their division into classes; but as all the parts of their organization are not yet well known, those sections cannot be characterized with as much precision as those of · the preceding divisions. In As·terias and Ursinus, called EcHINODERM:Es by Brugiere on account 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 Holothorire were necessarily united to them on account of the analogy of their internal organization, which is per"haps still more compJex, 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 usua11y 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 suspended 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 |
