280 [October, 



and still others, more numerous, found as parasites in the body of other animals. 

 Those which lead a permanent parasitical life, constitute now the genus Filaria, 

 of the same author,* which has been admitted by all subsequent naturalists, and 

 more than forty species of these are described by Rudolphi.t But there has been 

 a general belief, that the only difference between Gordius and Filaria consisted 

 in their habits, no zoological characters having as yet been detected. 



Lamarckf even says, that the species of Gordius were probably Filaria;; and if 

 he has kept those two genera, it was merely in accordance with a prevailing 

 practice. 



Cuvierll places Gordii at the end of the annelids, thus made to follow the 

 leeches, remarking, however, that they might perhaps come nearer the intestinal 

 worms. He was unacquainted with the fact, since ascertained, that several 

 Bpecies of true Gordius may be found, at a certain season of the year, within the 

 body of other animals. 



The genus Filaria is placed, by the same author, at the head of intestinal 

 worms. Its characters are derived from the external appearance, which, how- 

 ever, he (Cuvier) acknowledges, resembles closely that of Gordius. 



Should a generic difference hereafter be found between Gordius and Filaria, in 

 their anatomical structure, and we think it very likely to be the case, besides the 

 difference of embryonic development which already distinguishes them, we shall 

 have that peculiarity in their habits which makes Filaria to occur in such cavi- 

 ties of the body of other animals having no communication with the exterior, 

 whilst Gordii, when occasionally found within other animals, occur in the intes- 

 tinal canal ; that is to say, in a cavity which communicates directly with the 

 surrounding medium. This fact is of no small importance. 



The letter of Mr. Jacobson, to de Blainville, relates to Filaria, and not to 

 Gordius, as its title would lead any one to believe. 



Mr. Charvet,lT in describing two species of true Gordius, thinks that these 

 worms are indifferently external and internal, and that the distinction made be- 

 tween Filaria and Gordius becomes thus insignificant. Bot he is inclined to 

 believe that, if it can be proved that Filariae have a mouth provided with a suck- 

 ing apparatus, the character would be generic. He was not prepared, by direct 

 observations, to decide upon this fact. 



Leon Dufour** alludes to Gordii, and rejects the idea of an identity between 

 them and Filarias, considering the first as true Annelids, and the second as true 

 Entozoa ; there existing, he says, a mere external resemblance, which can only 

 be proved to depend on identity of structure by anatomical investigations. 



* O. F. Midler, in Naturforscher. Vol. xxii., 1787. 



t Entozoorum sive vermium intestinalium Historia Naturalis. (3 vol. Svo., 

 18081811), Vol. ii. p. 55 et seq. 



f Histoire naturelle des Animaux sans vertebres. Vol. iii., 1809, p. 670. 



II Le Regne Animal distribue d'apres son organisation, vol. iv., 1817, and 2d 

 ed. vol. iii., 1829. 



Extrait d'une lettre adressee a Mr. de Blainville sur le dragonneau. Ann. 

 Sc. Nat. 2de serie i. 1834. p. 320. 



ir Nouvelles Annales du Museum d'histoire naturelle. Vol. iii. 1834, p. 37. 



* A.nnales des Sciences Naturelles, 2de serie, vol. vii., 1837, p. 7. 



