34 INTRODrCTION 



circulation ; their resjiiratory organs are almost always on tlie surlace of the body ; 

 the "-reater 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 dismemberment of the Radiata of Cuvier, which 

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

 most naturahsts and comparative anatomists. J 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 from 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 

 systera."§ 



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 Cams (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- these various classes under three grand divisions, each of wiiich is 



inals into two classes, the Insects and Worms. I was the first to attack comparable to that of the vertebrate animals, 



this method, and presented anotherdivision,inaMemoirread before the f Synopsis Entozoorum, p. 572. 



Natural History Society of Paris, on the 10th of May, 1/95, and printed J Lamarck observes -.—"The ^;</7Mf«c Animals," (as he terms the 



in the Dicade Philusophiijue, in which I marked the characters and Acrita,) " have been very improperly called Zoop/iy^fj ; as their nature 



limits of the MoUusks, Crustaceans, Insects, Worms, Echinoderms, l is completely animal, and in no respect vegetable. The denomiua. 



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



in a memoir read before the Institute on the 31st of December, 1801. I portion of them.— ^nim. jam Ferftirfj, i. p. 890. 



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



primed miiie AnnahsdiiMus.d'llist. Nat., Xom. xix., I distributed ' the succeeding passages are also abridged.— Ei>. 



