34 INTRODUCTION.. 



circulation ; their respiratory organs are almost always on the surlace of the bod*' ; 

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

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

 sensibility.* 



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

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

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

 munity of structure in either the locomotive, excretive, digestive, sensitive, or generative 

 systems, with respect to this division, as it now stands in the Regne 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 /rom the higher division, in which these are always distinctly traceable, 

 either 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 parietes, 

 being simple excavations or passages in the granular pulp 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 nematoneurous 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.] 



• Before my time, modern naturalists divided all invertebrated ani- 

 mals into two classes, the Insects and Worms. I was the first to attack 

 this method, and presented another division, in a Memoir read before the 

 Natural History Society of Paris, on the 10th of May, 1795, ana printed 

 in the D&cade Philosophique, in which I marked the characters and 



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

 comparable to that of the vertebrate animals. 



t Synopsis Eritozoorum, p. 572. 



t Lamarck observes : — " The Apathetic Animals," (as he terms the 

 Acrita,) " have been very improperly called Zoophytes ; as their nature 



limits of the Mollusks, Crustaceans, Insects, Worms, Echinoderms, . is completely animal, and in no respect vegetable. The denemina. 



and Zoophytes. I distinguished the red-blooded worms, or Annelides, tion of Rayed Animals is also objectionable, as it applies only to a 



la a memoir read before the Institute on the 31st of December, 1801. portion of them. — Anim. sans Vertebres, i. p. 8!)0. 



And finally, in a Memoir read before the Institute in July, 1812, and I § Cyclopadia of Anatomy and Physiology, Ait. Acrita ; from which 



printed in the Annates du Mut. d'Hitt. Nat., torn, xis., 1 distributed the succeeuing passages are also abrdged.— Ed. 



