ON ANNELIDA. 
71 
with difficulty, in the furrows which separate these pedun- 
cles. 
In the pectinariag these vessels are placed in the same man- 
ner ; but they are only two pairs in number, situated in front, 
and adhering to the peduncles of the second and third pair of 
feet, behind the gills. The liquor which they contain is, ac- 
cording to Pallas, of a yellowish colour, like bile. 
The male part in the nereides is perhaps formed by a series 
of corpuscles, ranged by pairs on each side of the nervous 
cord, but only for the first three and twenty rings, diminish- 
ing in volume by little and little, in proportion as they ap- 
proach from the middle part more and more to the extremi- 
ties. It does not appear, however, that any canals arise from 
these organs, which should establish a communication be- 
tween them, and still less any communication with the ex- 
terior. 
The nervous system in all the chetopoda consists, as in all 
the articulata, of a series of ganglia, situated in the medio- 
ventral line, in as great a number as the body is composed of 
rings, often naked in the visceral cavity, but often also under- 
neath a portion of the sub-cutaneous muscular stratum. Each 
of these ganglia is united to the following by a double cord, 
very distinct, which constitutes an uninterrupted thread from 
one extremity to the other of the animal, enlarged at in- 
tervals. It is from these enlargements that subsequently pro- 
ceed in radii the threads which go to distribute themselves, 
especially to the fibres of the muscular stratum, whether it be 
sub-cutaneous or sub-mucous. The first, a little thicker than 
the others, does not appear to furnish more than two thick 
branches, which proceed from each side of the head, and 
which, arrived at the root of the tentacular cirri, are divided 
into threads for each of them. This is particularly observable 
in some nereides. 
