MOTION. 
curious spectacle of globular bodies moving 
in direct opposition to the force of gravity. 
The structure of this interesting animal in a 
mechanical point of view is worthy the pro- 
found attention of the mathematician, as well 
as of the anatomist and physiologist. 
Sect. IV. Annelida—tThe terrestrial An- 
nelides, such as the Lumbrici or Earth-worms, 
have the body cylindrical, and divided into up- 
wards of one hundred and twenty segments, 
which permit of extension and contraction, with 
the power also of curving the trunk vertically 
and horizontally, according to the play of the 
muscular system. The progression of the 
Lumbrici is aided by their retractile sete, or 
conical spines, eight of which are attached to 
each ring, consequently there are as many or 
more than 8 x 120 = 960 of these sete in 
a single worm, to assist its locomotion. As 
many of the Lumbrici attain the length of 
nearly twelve inches, there must be about twelve 
tings or segments in an inch of the body 
taken longitudinally ; now each ring being arti- 
culated with great freedom of motion, and the 
integuments being soft, flexible, and elastic, the 
trunk possesses very great mobility. 
The locomotion of the Lumbrici is simple, 
and performed in the following manner. When 
the animal is about to advance, the head is 
raised, and about fifteen or twenty of the an- 
terior segments are extended and placed firmly 
upon the plane of position ; the sete and rings 
assist in fixing the segment in advance ; this 
being effected, the next fifteen or twenty rings 
are drawn forwards, and the sete are again 
fixed in a similar manner; subsequently a third 
and fourth series successively complete the pro- 
gression of a step. The space taken at each ad- 
vance depends on the energy and magnitude 
of the animal, and the nature of the surface on 
which the movements are performed. Some 
Lumbrici, about six inches in length, having been 
placed upon a smooth surface, performed a 
distance equal to their own length at six or 
seven complete steps, taking about one inch at 
each advance; this occupied nearly one mi- 
nute of time, being a velocity of progression of 
about thirty feet per hour. ‘The smoothness of 
the surface retarded the celerity of their move- 
ments in consequence of the sete being inca- 
pable of fixing the segments against any points 
with sufficient power to enable them to draw 
the succeeding segments forward; under these 
circumstances the mouth was observed to be 
substituted, and to lay firm hold of the surface, 
whilst the anterior segments were drawn for- 
wards. The Lumbrici are capable of ascend- 
ing a plane inclined at an angle of 45° to the 
horizon, provided its surface presents suffi- 
cient irregularities for the application of the 
rings and sete. The centre of gravity of the 
‘Lumbrici is very near the middle of their 
length. The cylindrical form of the articulata, 
and the minute dimensions of the sete, render 
them (with such a limited basis of support) 
very liable to turn upon their axis, and roll 
over on their backs, but they readily recover 
the pendent position of the abdomen by bend- 
ing the trunk forwards into an arch, with its 
441 
convexity resting on the plane of motion, and 
the head and anus raised above it, but inclined 
to one side: the inclined direction of the raised 
segments causes the animal to revolve on its 
axis, and regain its natural position. 
When irritated, the Lumbrici contract and 
contort the body into curves resembling in 
form the letter S; they appear capable of con- 
tracting the body to one half of its entire length ; 
in which condition the integuments present a cor- 
rugated appearance. The Nais and Naiades are 
swimmers. The Hemocharis walks like the 
caterpillar of the Geometra. The Hirudines, 
or Leeches, are more developed in a transverse 
direction than the Lumbrici ; in these animals 
the mouth is surrounded by a lip, and the 
anal extremity is furnished with a flattened 
disc, each of which is capable of causing a 
vacuum, and the head and anus being fixed to 
the plane of position, whilst the body is elon- 
gated and contracted alternately, the locomo- 
tion is effected. Leeches are well known to be 
capable of thus ascending vertically upon the 
smooth surface of glass, to which they adhere 
with considerable force. 
Insecta. Apode larve of Insects —The num- 
ber of segments which compose the lengthened 
cylindrical form of the Apode larve and the dis- 
position of the muscular system permit the trunk 
to be moved in various directions ; to be elon- 
gated, contracted, curved upwards, downwards, 
or on either side, thus contributing to the pro- 
gression of the Apodes. The cephalic, thoracic, 
and abdominal sections, which may be consi- 
dered as merely auxiliary organs in animals 
furnished with arms and legs, are employed by 
the cylindrical Apodes as the sole instruments 
of locomotion. 
The progression of the Balaneus Nucium, the 
Maggot of the hazel-nut, is thus performed. 
Having first laid hold, with the mouth, of some 
point in the plane of position, the body is con- 
tracted and curved upon itself, and the anal 
extremity drawn forwards ; the latter then takes 
a fixed point for a fulcrum, and the segments 
which had previously approximated during the 
contraction, are again separated in succession 
from behind forwards, causing a slight undula- 
tion of the body in successive curves, vertical to 
the plane of motion. The head having been pro- 
jected forwards by the elongation of the trunk, 
repeats the same actions, recurring as before, 
in succession. Their progression is slow and 
laborious, each step not being more than from 
one-twelfth to one-fourteenth of aninch. The 
Cionus Scrofulariz, like the common Snail, 
secretes a slimy substance which enables it to 
walk on the leaves of the figwort, on which 
it feeds.* The larve of the Muscide are pro- 
vided with unguiform mandibles, with which 
they maintain a firm hold, whilst the body is 
contracted and dragged forwards. Other larve, 
as the Syrphus, use their mandibles for the 
same purpose.t 
Pedate Larve.—Many of the pedate larve 
of insects are furnished with six legs like the 
* De Geer, vol. v. p. 210. 
+ Kirby and Spence, vol. ii. p. 272. 
