188 FOURTH REPORT— 1834. 



Bull, de la Soc. Phil, for 1818. He divides them into three 

 orders, the characters of which are drawn from the similarity or 

 dissimilarity of the segments of the body with relation to the 

 appendages, and the more or less marked separation of these 

 segments into head, thorax, and abdomen. It is not necessary 

 to give the names of his orders, as he has changed them in a 

 more recent dissertation on these animals published in the 

 Diet, lies Scien. Nut. *, and to which I refer the reader for 

 a full development of his views respecting their organization 

 and arrangement. 



The memoirs of MM. Audouin and Edwards on the Annelida, 

 which are the most recent, and at the same time the most 

 valuable that have yet appeared, are contained in the Annules 

 des Sciences for 1832-33. These acute observers liave not only 

 discovered a vast many new species, but found some exhibiting 

 such peculiar characters, as render it necessary to institute 

 several new groups, and to remodel entirely the classification of 

 former authors. They remark that the system of Cuvier, although 

 adapted to the small number of species then known, cannot be 

 employed for the arrangement of many which have been since 

 discovered, without entailing violations of natural affinity. In 

 fact, they find that the presence or absence of the appendages 

 termed branchice does not by any means constantly coincide 

 with the true characteristic marks of the different types of 

 organization presented by these animals, and that moi'e than 

 one instance might be adduced of species presenting these two 

 modifications of structure, yet identical in all other respects, 

 and indisputably belonging to the same family, if not to the 

 same genus. The systems of Savigny and Blainville they state 

 to be attended by similar difficulties. What they pi-opose is, 

 instead of confining their attention to the hrancliicB only as the 

 basis of their classification, to take into account the different 

 membranaceous appendages in general, the consideration of 

 which will lead to more natural divisions. It would seem indeed 

 from their researches, that although the branchiae are occa- 

 sionally much developed, so that it is impossible to mistake their 

 function, or to confound them with the cirri and tentacula, yet in 

 other cases respiration is carried on by some of the other mem- 

 branaceous appendages, all of which take up this function by 

 turns in different cases. Hence by considering these organs col- 

 lectively, and attaching the same value to all of them, we shall 

 obtain characters of the first importance for the classification of 

 the Annelida. It is accordingly from these organs, which the 



* toin. Ivii., Art. Vers. Also published separately under the title of Manuel 

 d' Helminlhohgie. 



