34 



INTRObL'CTION, 



circulation ; their respirator^' 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," writes Mr. Owen, " for a (lismeml)erment of the Radinta of Cuvier, which 

 Rudolphi justly calls a chaotic groupt, has l)cen felt, and directly or indirectly expressed, by 

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

 mimity of structure in either the locoraoti\'e, excretive, digestive, sensitive, or generative 

 systems, with respect to this division, as it now stands in the Regne Anunal. * * * 



" 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 ^vhich these are always distinctly traceable, 

 eitlier radiating from an oral ring, or distriljuted in a parallel longitudinal (hrection, 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 



AciiiTE Animals (Anlmalia acrita) 



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

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

 that the alimentarj' cavity and sanguiferous canals are destitute of proper parietes, 

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

 Nematoneiira (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 wliich 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 rc]iroduction are common in the acrito division. Some 

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



* fieforc my time, moilcrn naturftlist.'. diviilcd all inverlLbratcd ani- 

 inals into two classeit, the lijsects and Worms. I was tlie first to attack 

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

 \aturul History Society of Paris, on the 10th of May, )/95, and jirinted 

 in the VtciLde Philu3'ipliiqitf, in wliich I marked the characters and 

 limits of the Mollaslis, Crastaceaiis, lasectB. Worms. Ecliinoderms, 

 (lad Zo.iphytes. 1 distiii^ruisiied the red-blooded worms, or AnneJides, 

 ;.-. a menjoir read before the Institate on the 31st of Ueeember. 18U1. 

 And tin.illy. in a ^remoir read before the Institute in Julv. ISli, and 

 printed in tlie Jn.nul^i liu Mus. d'llul. A'u/., torn. xL\., J distributed 



portion of thorn. — Atiiin. anus F'erlibrfs, i. p. ?itO. 



5 Cyr/opetdiii of Anatotii;/ iind Phi/siolo^, Art. . 

 the iuccecuij]|r pabiujos lu-c iviso aljr'iJ|,'tJ. — Ed. 



