ARTICULATA., §5 
very much in their development, and the segments are very distinct. 
A few only of the lowest Articulata, of which the earthworm may be 
taken as an example, have no distinct head, and no eyes nor other organs 
of special sense. Some of them have the mouth adapted merely for 
suction ; but others have jaws or mandibles, and frequently several pairs 
of them, for seizing their food and tearing it in pieces. Their jaws do 
not open vertically, as in vertebrated animals, but laterally. There is no 
proper heart, but instead of it a dorsal? vessel, which runs along the central 
line of thé body near the back or upper side. Respiration is effected by 
gills in those Articulata that live in water; but in those that live in air, 
by air-tubes, which ramify through the whole body, as in insects, or by 
mere air-sacs, as in the earthworm. 
Annelide.— Many of the lowest Articulata have no limbs, but locomo- 
tion is accomplished by mere contraction and extension of the body. An 
earthworm, pushing its way forward, draws in the hinder part of its body 
as much as possible, the rings closing together, and then stretches out the 
fore-part as far as the integuments will permit. The earthworm belongs 
to a class called Annelide or Anmelids, from Latin annulus, a ring. 
They have all very much the same form, and none of them have limbs, 
but many, higher in the scale of organisation, than the earthworm, have 
eyes, and some have feelers or tentacles. Most of them live in water and 
respire by gills. , 
Leeches belong to an order of Annelids differing from all the rest in 
their mode of locomotion, which is by means of suckers, one at each end 
of the body. The sucker at the fore-end of the body is also the mouth ; 
and that of many species is admirably adapted not only for killing and 
eating the minute aquatic animals which constitute their ordinary food, 
but for making little wounds in the higher animals, when opportunity 
occurs, through which their blood may be sucked. 
Myriapoda.—Next to the Annelids may be ranked the class called 
Myriapoda,?* in which the same elongated form generally prevails, 
and the body is, in like manner, composed of a large number of almost 
equal rings. All the Myriapoda, however, have a distinct head, most of 
them have eyes, and they have antenne like those of insects. The 
mouth is furnished with a complete masticating apparatus. The body 
is protected by a hard covering, or external skeleton. None of the 
Myriapoda have wings. They do not undergo so great transformations as 
insects, but issue from the egg somewhat like what they are ultimately to 
become. The higher kinds of Myriapoda, as Centipedes, feed on animal 
substances, or prey on small animals ; the lower, as Gallyworms, gencrally 
feed on decaying vegetable matter. 
1 From Latin dorsum, the back. 
2 rom Greek myrios, ten thousand, and pous, podos, a foot. 
