ON ANNELIDA. 
97 
Leaving systematic distribution, however, for the present, we 
must now give a succinct view of the structure and history of 
the nereides. 
The body of the nereides is in general extremely elongated, 
slender, attenuated, cylindrical, sub-cylindrical, or even 
sometimes depressed, especially underneath. Finally, a little 
broader in the middle, it becomes gradually attenuated to- 
wards the extremities, but much less so towards the anterior 
extremity, which is always more or less truncated, than to- 
wards the posterior. It is formed of a great number of rings, 
or segments, broader than long, very distinct, very mobile, 
one upon the other, in their whole circumference, and the 
broadest and longest of them are in general towards the an- 
terior third of the body. The posterior ones decrease insen- 
sibly as far as the last. On the first or second anterior ring 
we may pretty frequently distinguish one or two pairs of 
black orbicular spots, which have been regarded as eyes. 
These first rings, in certain species, do not appear to be com- 
plete, but rather cleft, or open in their inferior part, so that 
the aperture of the oesophagus is preceded by an oblique in- 
ferior cleft, to which the name of mouth has been given. In 
other species these rings are complete, but they are wide 
enough to permit the re-entrance of a considerable cephaloi’d 
proboscis ; which itself is sometimes composed of one or two 
rings. 
To suit to this disposition of the cephalous rings, it is 
evident that the mouth must present different forms. In the 
first case, it is a cleft more or less long ; in the second, it is a 
round hole, sometimes accompanied in its circumference with 
papillm, or papillary tubercles disposed in radii. 
The posterior extremity of the body of the nereides ter- 
minates by being very much flatted. Sometimes the last ring 
is in the form of a dagger point, which alone extends beyond 
the anus. This last is always very broad and transverse. 
VOL. XIII. 
11 
