ox ANNELIDA. C5 



more complicated, and capable of bemg earned 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 w^hich 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 



