Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25759/178/
ANNELIDA. 
genera Serpula, Sabella, Terebella, Amphitrite 
Hermella, and Siphostoma.) 
Third Order.—Annelida terricola. 
Body, completely destitute of soft appendages. 
Jfeet, scarcely or not at all distinguishable, and 
represented only by some bristles. 
Head not distinct, without eyes, antennae, or 
jaws. 
This order comprehends the genera Clymena, 
Lumbricus, Nais, fyc. 
In the classification of M. Cuvier it is united 
to the Hirudinida to form the order Anne- 
lides abranches. 
Fourth Order.—Annelida suctoria. 
Body destitute of bristles for locomotion, com¬ 
pletely apodous, and without soft appen¬ 
dages. A prehensile cavity in the form of a 
sucker at each extremity of the body. 
Head, not distinct, but generally provided with 
eyes and jaws. 
This order is composed of the family of Hiru¬ 
dinida, and of the genus Branchellion. 
External conformation.—The Annelida have 
always an elongated, generally cylindrical, and 
vermicular form; sometimes, however, they 
are flat or more or less oval. The body is com¬ 
posed, as we have already observed, of a series 
of rings, not of a horny or calcareous texture as 
in the majority of insects and Crustacea, but 
membranous and separated from each other 
only by a transverse fold of the integument; as is 
seen in certain larvae. The* number of these rings 
is occasionally very considerable (some nereida 
have more than 500), and in many annelida it 
varies considerably in different individuals of 
the same species, and seems to increase with age. 
In some instances these segments are sub¬ 
divided into two or more transverse bands by 
furrows. 
In general each ring supports a pair of mem¬ 
bers, and when an apparently single segment 
gives origin to a greater number of these or¬ 
gans, it is easy to perceive that it results from 
the union of many rings blended together. 
The two extremities of the body are sometimes 
dilated in the form of suckers (in the suctorious 
annelidans), but in general nothing of the kind 
exists, and the anterior extremity either resem¬ 
bles the rest of the body, or it terminates in a 
head more or less distinct (as in the nereida, 
see fig. 62), often supporting eyes (a), and fili- 
Fig. 62. 
form appendages called antennæ, (b,c), the num¬ 
ber of which is generally three, four, or five. 
The mouth is situated at the extremity of the 
body, and in the acephalous annelida is di¬ 
rected forwards, but in the cephalous species 
this opening is situated below the base of the 
head. The anus is placed at the opposite ex¬ 
tremity, and is almost always found on the 
dorsal aspect of the body. A certain number 
of Annelida are completely apodous, and do 
not present the least trace of an appendage on 
any of the segments of the body (the hirudinidæ). 
Others exhibit on either side many rows of 
bristles, which fulfil the office of feet (the terri- 
colæp In others, again, the bristles of which 
we have spoken are supported on a fleshy 
tubercle more or less prominent, and more or 
less complicated in structure, and to these 
organs the name of feet is applied. 
The feet of the Annelida, when they present 
the maximum of development of which they 
are susceptible in that class of animals, are com¬ 
posed each of two very distinct portions, placed 
one above the other, and appertaining the one to 
the dorsal, the other to the ventral arch of the 
ring. (See fig. 63,which represents one of the feet 
Fig. 63. 
of an amphinome.) M. Savigny, who was the 
first to study with due care the zoological cha¬ 
racters furnished by these appendages of the 
annelida, gave to these portions of the feet the 
names of dorsal oar (a) and ventral oar (5) (rame 
dorsal et rame ventral). Sometimes these oars 
are pretty distant from one another, {fig. 63.) 
sometimes they are separated only by a shallow 
fissure {fig. 64. which represents the foot of a 
nereid), and occasionally they are so intimately 
blended together that they can hardly be dis- 
Fig. 64. 
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