ON ANNELIDA, 
(>5 
more complicated, and capable of being carried forward or 
backward, by fasciculi of muscles, which, belonging to the 
sub-cutaneous muscular stratum, are carried, either from the 
anterior margin of the buccal orifice, to the anterior half of its 
mass, or from the rings which immediately follow it behind, 
to its posterior half. We find, besides, that it is in a great 
measure composed by numerous transverse fibres, which must 
act strongly in mastication. 
This mastication is performed by corneous or calcareous 
parts, which cover some longitudinal folds, corresponding to 
each other by pairs, and they often extend a considerable 
way into the entrance of the intestinal canal. The number 
and form of these various kinds of teeth varies sufficiently. 
No true odd one exists among them, that is to say, in the 
middle dorsal or ventral line ; but almost always the two teeth 
which constitute the inferior pair, are contiguous, in the medial 
line, which forms a sort of under lip. The lateral pairs are 
variable in number, and most frequently composed of a sort 
of handle which is introduced into the muscular stratum, and 
of a free curved part, which may be either denticulated or not. 
It is this last part, which, being susceptible of being some- 
times augmented at one of its angles by a corneous tubercle, 
has been the cause, that M. Savigny has defined, in a group 
or two of the nereides, some of the genera which he has esta- 
blished among the multidenticulated species, according to the 
odd or even number of these organs, which he has deno- 
minated jaws. M. de Blainville declares that he has found 
them always even, with the difference just noticed,— and 
which does not take place constantly on the same side, as 
M. Savigny supposed, but in an entire genus, that of aphro- 
dite, the teeth which constitute the upper and lower pair, are 
contiguous, and touch each other in the middle line, from 
which it results that they act, like the jaws of bony animals, 
in a vertical direction, two against two. 
VOL. XIII. 
F 
