22 INTKODUCTION. 



circulation ; their respiratory organs are almost always on the surface of the body ; 

 the greater number have only a sac without issue, for the whole intestine ; and 

 the lowest families present only a sort of homogeneous pulp, endowed with motion and 



sensibility.* 



[" The necessity," v.Tites Mr. Owen, " for a dismemberment of the Radiata of Cuvier, which 

 Rudolphi justly calls a chaotic groujif* has been felt, and directly or indirectly expressed, by 

 most naturalists and comparative anatomists.^ It is impossible, indeed, to predicate a com- 

 munity of structm-e in either the locomotive, excretive, digestive, sensitive, or generative 

 systems, viith respect to this division, as it now stands in the Re(/ne Animal. * * * 



" Taking the nervous system as a guide, the Radiata of Cuvier will be found to resolve them- 

 selves into two natural groups, of which the second differs in the absence or obscure traces of 

 nervous filaments from the higher division, in which these are always distinctly traceable, 

 cither radiating from an oral ring, or distributed in a parallel longitudinal direction, according 

 to the form of the body. 



"These different conditions of the nervous system are accompanied by corresponding 

 modifications of the muscular, digestive, and vascular systems ; and a negative character, appli- 

 cable to the higher division of Cuvier's Radiata, may be derived from the generative 

 system."§ 



It is only in the lower-organized of these divisions, to which the term 



AcRiTE Animals (Animalia acrita) 



has been applied by Macleay, also that of Protozoa and Oozoa by Carus (from the 

 circumstance of its members being analogous to the ova or germs of the higher classes), 

 that the alimentary cavity and sanguiferous canals are destitute of proper jjarietcs, 

 being simple excavations or passages in the granular jDulp of the body : for in the 

 Nematoneura (a name applied to the higher division of Cuvier's Radiata by Owen), the 

 digestive organ is provided with a proper muscular tunic, and floats in an abdominal 

 cavity : and those classes which manifest a circulating system distinct from the diges- 

 tive tube possess vessels with proper parietes, distinguishable into arteries and veins. 



No ncmatoneurous class presents an example of generation by spontaneous fision or 

 gemmation, but these modes of reproduction are common in the acrite division. Some 

 of the latter, however, are oviparous ; and in a few the sexes are separate.] 



• ncfore my time, motlcrn naturalists diviiictl all iiivcrtcbratcd ani- 

 mlt Into two cinsaca, the Insects and Worms. I was llic first to attack 

 Ihla method, and iiresentcd anuthur division,!!! a Memoir read before the 

 Natural llintorx Society of Paris, on the 10th of May, 17S)5, and iiri!!tcd 

 In the JUciide I'hili.iophiijur, in which 1 marked the characters and 

 llmith of the Mollasks, Crustaceans, l!i5ccl», Wonns, Kchinodcrms, 

 and /oo|ihyl.-a. I di»tini;ui»hcd the red-blooded worms, or Annclides, 

 Jo « memoir read hcforc the Iiialitulc on the 31st of December, ISOl. 



these various classes under three grand divisions, each of which is 

 comparable to that of the vertebrate animals. 



t Synopsis Etitoxoorum, p. 5/2. 



t Lamarck observes : — ■' The ytpatlulic Animals," (as he terms the 

 ^critfi,) '* have been very improperly called Zoop/n/tes ; as their iiature 

 Is completely aniinal, and in no respect vegetable. The denomina- 

 tion of Itnyrd j-luimuls is also objectionable, as it applies only to a 

 portion of them. — ^litiin. satis f'ert^bres, i. p. B90, 



And Snnlly, in a .Memoir read before the Institute in July, 1812, and i § Cydopadia of Aiidlumi/ and rhiiaiuhtii/iAn. j'IcrUa ; fron! which 

 rrlnlcd \fHhi:.lnnalcsduUm.d'Hist. Nat., lorn, xix., 1 distributed | the succeeding poss-iges are also obridi;cd.—Ko. 



