ON ANNELIDA. 103 



on which it is supported a slight excavation ; this side is 

 white, and evidently in communication with the rest of the 

 system. 



The locomotive apparatus of these animals is extremely 

 simple, although considerable : it is composed by two strata 

 of muscular fibres, situated under the skin ; the external 

 stratum, much thinner than the other, is formed by transverse 

 fibres, while the internal one, very thick, is entirely formed by 

 longitudinal fibres ; this last stratum is much thicker under- 

 neath, where it constitutes two or four narrow bands, 

 extended from one extremity to the other, and sometimes per- 

 ceptible externally ; on the upper part, or in the dorsal line, 

 the longitudinal band is perhaps not thicker, but it is not much 

 divided except into two, by a medial furrow ; on each side 

 the muscular bands, superior and inferior, are thicker, so as 

 to fill almost all the interval comprised between the skin and 

 the intestinal canal. It is in fact from these bands that pro- 

 ceed the small oblique muscles which go to the root of each 

 appendage ; and it is in their thickness that are deeply sunk 

 the fasciculi of set^, and of aciculi, of those appendages, 

 which are provided with them so as to be drawn forward or 

 backward by the fibres which are attached to their base, or 

 which penetrate even into the nipples which support them ; 

 these are true specific muscles. In the species in which the 

 appendages are deeply divided into two branches, there is be- 

 sides a longitudinal muscular fasciculus which follows the 

 whole lateral line, and to which the transverse fibres adhere. 



It is not necessary to say that all the longitudinal muscles 

 are divided into as many parts as there are rings to the body 

 of the animal : in the species which have a pair of teeth, each 

 of the latter has peculiar muscles to approximate and remove 

 it ; in those whose masticatory apparatus is more compli- 

 cated, the muscles are more complicated : at first the upper 

 lip, or the cleft ring, which immediately precedes the mouth, 



