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. Duges 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 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, and Annelida suctoria (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 ERR ANTI A.
Body, with soft appendages (cirri, branchize, or antenna), generally disposed over the whole length of the animal, and not collected towards the cephalic extremity.
°Feet generally very distinct, armed with seta: or bristles, which have very rarely the form of hooks.
Head generally distinct, and provided with eyes, antenna, 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, dontes, Acoetes, Sigalion, Palmyra, Amphinome, Chloeia, Euphrosyne, Hipponoe, Eunice, Onu ph is, Diopa tra, Lysidice, Enone, Nereis, Syllis, Hesione, Alciope, Myri ana, Pleyllodoce, Nephtys, Goninada, Glycera, Aricia, Aonis, Ophelia, Cirrhatulis, Peripatus, Chetopterus, Arenicola.) Second Order.—ANNELIDA 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, antenna, pro tractile proboscis, or jaws.
(This order corresponds to that established by Cuvier under the same name, and includes the genera Serpula, Sabella, Terebella, Amphitrite, Hermella, and Siphostonia.) Third Order.—ANNELIDA TERRICOLA• Body, completely destitute of soft appendages. Feet, scarcely or not at all distinguishable, and represented only by some bristles.
Head not distinct, without eyes, or jaws.
This order comprehends the genera Clymena, Lumbricus, Naas, 4-c.
In the classification of M. Cuvier it is united to the Hirudinida to form the order Anne lides abranches.