ON ANNELIDA. 99 



accompanied with an augmentation of another part, which 

 produces what have been named antennular cirri, tentacula 

 and antenna, by the great development of the sensitive part 

 of the appendage, on the cephalic rings, and by their superior 

 position, in the same way as the agglutination of the setse, or 

 of the aciculi on the lateral parts of the anterior rings, has 

 constituted what has been named jaws, or teeth, at least in 

 the species which have them corneous and simple. Finally, 

 to this same augmentation of the tentacular cirri of the ap- 

 pendages, is owing the long pair of setaceous filaments 

 which seem to terminate the body behind, forming a sort of 

 tail. They are always double, and constantly belong to the 

 ring before the last. 



The attachment of the appendages in the nereides still 

 presents something remarkable enough, in this, that being 

 nearly lateral in the medial or normal rings, it descends a 

 little in the more posterior ones, and ascends again, much 

 more evidently in the anterior, so that what remains on the 

 cephalous rings, namely, the tentaculary filaments, are almost 

 altogether superior, and become frontal. In certain species, 

 even the two tentacula which are most approximated, form 

 but one, which is then odd and medial. 



From all this, it is evident that we may distinguish, and 

 with just reason, to a certain point in the body of a nere'id, 



1. a proboscis, which is but one or two entire anterior rings, 

 in the interior of which, there may be teeth, which, without 

 any doubt, become exterior, or at least marginal in their action. 



2, A cephalous enlargement, formed of two broader rings 

 than the proboscis, and disposed obliquely, so that the antei'ior 

 produces a sort of advance, or front, under which the pro- 

 boscis may withdraw, and the posterior, a complete ring, re- 

 ceives it when it is more deeply retracted. This it is which 

 gives to the incomplete appendages of these cephalous rings, 



H 2 



