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 seta), 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 nereid, 
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 anterior 
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, 
