78 
SUPPLEMENT 
animal, whose anus is always terminal and posterior, and 
which, besides, has no sort of adherence with its tube. 
The genus Serpula may be thus characterized : animal 
moderately elongated, a little depressed, composed of a great 
number of articulations very much crowded, consisting of an 
abdomen and ceplialothorax, tolerably distinct ; the head, or 
first segment, is larger than the others, and has for appendages 
above a pair of elongated tentacula, dilated into an operculi- 
form disk, radiated at the extremity, and one of which alone 
is completely developed. On each side is a tolerably large 
gill, in the form of an unilateral comb, composed of a variable 
number of long cirri, furnished with a double internal rank 
of mobile barbs ; the thorax is short, with a sort of membrana- 
ceous sternal plate inferiorly ; the appendages of the thoracic 
and abdominal rings are divided into two oars, the upper one 
provided with a fasciculus of subulated setae, returning to- 
wards the back; the lower with a range of hooked setae, for 
the thoracic rings, but the reverse for the second. The testa 
is in the form of a conical tube, solid, entirely calcareous, irre- 
gular convoluted, free in a portion of its termination, and fixed 
by its summit ; the aperture is rounded. 
The characters just assigned to the genus Serpulce, after the 
most common European species, will suffice to make known 
the general form of the animal, and all that presents itself ex- 
ternally in relation to it, adding, however, that it is contained 
in a membranaceous envelope, as arc all the tubicolae — an 
envelope which, without doubt, produces the shell, always 
much larger than itself. As to the organization of these ani- 
mals, it has been very little studied. 
The intestinal canal commences by a buccal orifice, alto- 
gether anterior, provided with two lips, without any trace of 
teeth or proboscis. This orifice conducts into the intestinal 
canal, which proceeds directly to the anus, is always mem- 
branaceous, and even presents no very distinct gastric en- 
