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 mostexternal 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- 
tractile 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- 
