326 THE NATUHAL HISTORY REVIEW. 



various groups of Worms, with a view, as far as possible, to avoid the 

 difficulties which arise from the differences of opinion to wliich refer- 

 ence has just been made. These groups are far from being equivalent 

 to one another. Each has, however, a well-defined existence in the 

 literature of zoology. For the present we shall not discuss their 

 mutual relations further than may be necessary to indicate the 

 position occupied by the parasitic worms in the animal kingdom. 



By Eudolphi,* these worms were brought together into a class, 

 to which he gave the name of Entozoa. 



Cuvierf associated with the Entozoa certain worms of free habit, 

 including the genera Planaria, JSFemertes, and their allies, which 

 Ehrenberg % and others have separated to constitute the group 

 Turhellaria. Cuvier also placed in the same division a few arthro- 

 pod parasites, now transferred to the Crustacea and AracJinida. The 

 whole were united into oue class, ' Les Intestinaux,' of his sub-king- 

 dom, ' Les Zoophytes ou Animaux E-ayonnes.' Another class, ' Les 

 Annelides,' together with the Insects of Linnaeus (sub-divided into 

 three classes), formed the sub-kingdom of ' Les Animaux Articules.* 



True to the principles of a morphological classification, Cuvier 

 was amply justified in not regarding the Entozoa, because of their 

 peculiar habit alone, as worthy to take the rank of a separate class. 

 And he was also right in perceiving the essential similarity of struc- 

 ture between this group and the Turhellaria, Did he err in his 

 estimate of the anatomical differences between the ' Intestina ' and 

 the Annelids, classes which are now seldom placed in distinct sub-king- 

 doms ? And yet, as we shall see, they agree with one another less 

 closely than many modern zoologists are woiit to suppose. 



De Blaiuville, with his usual sagacity, was one of the first to 

 poiut out the errors (?) into which both Eudolphi and Cuvier had 

 fallen. He it was who, in 1S1G,§ removed the Entozoa to the 

 Articulate sub-kingdom, and thus wrote of their mutual affi- 

 nities : 



" Sou&lenom d'Entozoaires, qui est evidemment mauvaispuisqu'il 

 " est tire d'une circonstance non inherente a I'objet, et qu'en outre 



* Entozoorum Historia Naturalis, vol. i. 1808. 



t Le Rcgne Animal, tome iv. 1817. See also tome iii. of his second edition, 1830. 



% Symbolce riiysicte, series prima, 1831. The Turhellaria, as first constituted, 

 did not include the Ncmertina, which De Quatrefages, Siebold, and Schultze after- 

 wards grou]icd with them. 



§ Prodrome d'une nouvelle distribution systematique du regne animal. 



