ANNELIDA. 



165 



&c., but is not received by all zoologists of the 

 present day. M. De Blainville, in his metho- 

 dical distribution of the animal kingdom, has 

 adopted another plan. Taking the exterior 

 organs for the base of his system, this naturalist 

 divides the articulate animals, which he terms 

 " Entomozoaires," into seven classes, of which 

 the penultimate, viz., the " chetopodes," com- 

 prehends the Annelidans provided with loco- 

 motive bristles, and of which the last, viz, the 

 " apodes," is composed of the Annelidans des- 

 titute of those organs, together with the planariae 

 and intestinal worms.* 



The general plan of organization exhibited 

 in the animals which are grouped together by 

 Cuvier under the name of " vers intestinaux," 

 and the numerous affinities which connect the 

 planariae and several helmintha to the Annelida, 

 appear to us fully to justify a partial adoption 

 of the innovations introduced by M. De Blain- 

 ville, and to indicate that the natural position 

 of the white-blooded worms is by the side of 

 those with red blood, at the bottom of the sub- 

 kingdom of articulate animals ; whilst in the 

 system of Cuvier the Annelida are placed at 

 the head of that great division of the animal 

 kingdom, and the entozoa are left among the 

 zoophytes. But, on the other hand, similar 

 reasons appear to us to oppose the adoption of the 

 divisions which M. De Blainville has proposed 

 for the articulate animals. That zoologist, in 

 fact, establishes a distinction between his che- 

 topoda and apoda as wide as between the former 

 and the insecta, arachnida and Crustacea, and 

 thus separates from the setiferous annelidans to 

 place among the intestinal worms the hirudines, 

 which approximate to the former and deviate 

 from the latter in many of the most important 

 points of their organization; for example, in the 

 existence of a gangliated nervous system. 



This arrangement does not appear to us to 

 accord with the spirit of a natural classification, 

 in which the several divisions ought to be in- 

 dicative of the different degrees of importance 

 which the modifications of the animal organiza- 

 tion present. 



In the present state of science the class An- 

 nelida ought in our opinion to be preserved 

 nearly as it was established by Cuvier, but 

 should be joined with the entozoa and rotifera, 

 to form a great division of the sub-kingdom 

 articulata, distinct from the natural group, con- 

 sisting of insecta, myriapoda, arachnida, and 

 Crustacea. The affinities, indeed, between the 

 setiferous annelidans and the hirudines are too 

 close to admit of their being arranged in sepa- 

 rate classes ; and, on the other hand, every day 

 discloses new facts of a nature which demon- 

 strate that the vermiform animals pass from 

 one to another by almost insensible gradations. 

 Thus the researches of M. Dtiges on the 

 planaria? show how closely their structure ap- 

 proaches that of certain red-blooded worms, and 

 the distinction founded on the colour of the 

 nutritious fluid no longer suffices to separate 



* See the Bulletin de la Soc. Philonaathique, 

 1818 ; De 1'Organization des Animaux par M. de 

 Blainville, torn. i. table 7 ; and the article Vers' of 

 the Dictionnairc dcs Sciences Naturelles, torn. Ivii. 



them ; for on the one hand it is proved that 

 the colour of the blood is yellow and not red 

 in some of the annelidans properly so called ; 

 while on the other hand I have recently ob- 

 served on the shores of the Mediterranean an 

 animal which differs from the genus prostoma 

 only in the possession of red blood. We now 

 know intestinal worms which have a circulation 

 and a vascular system as well formed as that of 

 the annelida, which they already resemble so 

 much by their outward form. The absence of 

 a rudimentary nervous system in the entozoa is 

 called in question by skilful anatomists. Lastly, 

 the excellent works of Ehrenberg on the in- 

 fusoria of the class rotifera prove the analogy 

 that exists between these minute beings and the 

 articulate animals generally, but more espe- 

 cially to the annelida. 



The differences which the annelida present 

 among themselves have necessitated their di- 

 vision into many secondary groups or orders. 

 In the latest work* that has been published on 

 the classification of these animals, they have 

 been divided into four orders, under the names 

 of Annelida errantia, Annelida tubicola, Anne- 

 lida terricola,smd Annelida auctoria (suceuses). 

 This classification is based on the combination 

 of the modifications which exist in the struc- 

 ture of these beings, and does not materially 

 differ from that proposed by M. Cuvier in the 

 Regne Animal, and by M. Savigny in the 

 great work on Egypt. 



The following is a table of the principal 

 characters which distinguish these groups. 

 First Order. ANNELIDA ERRANTIA. 

 Body, with soft appendages (cirri, branchiae, 



or antennae), generally disposed over the 



whole length of the animal, and not collected 



towards the cephalic extremity. 

 Feet generally very distinct, armed with sette. or 



bristles, which have very rarely the form of 



hooks. 

 Head generally distinct, and provided with eyes, 



antennae, and a retractile proboscis, often 



with jaws. 



(This order, which nearly corresponds to that 

 of the Annelida dorsibranchiata of Cuvier, com- 

 prehends the genera Aphrodita, Polynoe, Polyo- 

 dontes, Acoetea, Sigalkm, Palmyra, Amphinome, 

 Chloeia, Euphrosyne, Hipponoe, Eunice, Onu- 

 phis, Diopatra, Lysidice, Lombrinereis,Aglaura, 

 (Enone, Nereis, Syllis, Heaione, Alciope, Myri- 

 ana, Plu/llodoce, Nephfys, Goninada, Glycera, 

 Aricia, Aonis, Ophelia, Cirrhatulis, Peripatus, 

 Cfietopterus, Arenicola.) 



Second Order. ANNF.LIDA TUBICOLA. 

 Body, with soft appendages, for the most part 



collected together at the cephalic extremity. 

 Feet, almost always of two kinds, generally de- 

 prived of cirri, and armed with hooked bristles. 

 Head not distinct, without eyes, antennae, pro 



tractile proboscis, or jaws. 

 (This order corresponds to that established by 

 Cuvier under the same name, and includes the 



* See Classification des Annelides et description 

 des especes qui habitent les cotes de la France, 

 par MM. Audouiu et Milne Edwards, torn. ii. 

 des Recherches pour seivir al'Hist. Nat. du liitoial 

 de la France. 



