ON ANNELIDA. 123 



face of the first rings of the body, certain black points, which 

 have some apparent resemblance to the simple eyes of hexapod 

 insects, and still more so to the similar organs which exist in 

 the nereides ; but whether they are really eyes is more than 

 doubtful, for on examination they do not appear to possess 

 either the structure or the uses of such organs. 



As for an organ of hearing, the place of the leeches in the 

 animal series will not permit us to believe that they possess 

 any. 



The apparatus of locomotion consists in its active part 

 alone, and it is entirely confounded with the skin which 

 covers it ; thus it is erroneously that some authors have ad- 

 mitted that each ring of the body is supported by a cartila- 

 ginous band. The contractile fibre has a shining satiny 

 aspect. 



The distinct part of the muscular system forms a stratum 

 moderately thick at the internal face of the skin, on its whole 

 extent, but a little thicker underneath than above. This 

 stratum is composed of two planes — the external, formed of 

 circular or transverse fibres, is much more slender than the 

 internal. The latter is tolerably thick, especially below ; it 

 is entirely composed of longitudinal and fasciculated fibres, 

 the most external of which terminate from one ring to ano- 

 ther, while the internal have an extent much more consider- 

 able. We remark, moreover, certain fasciculi of transverse 

 fibres within the plane formed by the longitudinal fibres. 



At the anterior extremity of the body these two planes of fibres 

 appear, as it were, to be confounded, from which results a con- 

 ti'actile tissue, not distinct from that of the dermis, and which 

 constitutes the two lips or edges of the anterior aperture, there 

 susceptible of assuming any form. 



At the posterior extremity there is also a sort of confusion 

 of the two planes of muscular fibres, but they assume a new 

 and peculiar disposition ; in fact, the longitudinal fibres, ap- 



