The Annelides, say MM. Audouin and Milne-Edwards, which we group round the genus Aricia
of Savigny, and of which we form the fifth family in the order Errantes, present very considerable dissimilarities in their external structure, — a circumstance which ought not to surprise us, for whenever organs, hecause of their minor developement, become of slight importance in the economy of the animal, and are about to be obliterated more or less entirely from its anatomy, we find them to vary proportionably in their forms. Such is the case with the exterior appendages of the Ariciadae, a small family which intervenes to smooth the abruptness of the passage between the more typical An. Errantes, and the Annelides of the orders Terricolae and Tubicolae.
It is probably from this discrepancy among them that, up to this time, no naturalist has seized upon the characters which seem to us to unite them in one, but every one has scattered its members among different groups. Several of them have been considered as related to the Earth-worms, others to the Nereides, and a certain number have been collected together by M. de Blainville in his family "Nereiscoles." The end which that zoologist had in view in the establishment of that family is very nearly the same which has led us to unite in one distinct group the Annelides in question; and it is probable that if Blainville had personally observed a greater number of species, his opinions relative to the composition of the family
would have been more in unison with ours than they happen to be.
[None. Introduction as follows:]