ARTICULATA. 281 
pair of legs, of which the hindermost is converted into 
spines. They have longer antenne than the preceding, 
and the mouth is armed with two formidable fangs con- 
nected with poisonous glands. They are carnivorous and 
active. Such is the Centipede (Scolopendra). 
Ciass V.—Insecta. 
Insects are distinguished by having head, thorax, and 
abdomen distinct, three pairs of jointed legs, one pair of 
antenne, and generally two pairs of wings. The number 
of segments in the body never exceeds twenty. The head, 
apparently one, is formed by the union of seven pieces. 
The thorax consists of three, the prothorax, mesothorax, 
and metathorax, each bearing a pair of legs; the wings, if 
present, originate from the last two segments. The abdo- 
men is normally composed of nine segments, more or less 
movable upon one another. The skin is hardened with 
chitine, and to it, as in all Articulates, the muscles are at- 
tached. The organs of sense are confined to the cephalic 
division of the body, the motor organs to the thoracic, and 
the vegetative to the abdominal. All the appendages are 
hollow. 
The antenne are inserted between or in front of the 
eyes. There is a great variety of forms, but all are tubn- 
lar and jointed. They are supposed to be organs of touch, 
and also seem to be sensitive to sound. The eyes are 
usually compound, composed of a large number of hexago- 
nal corneze, or facets (from fifty in the Ant to many thou- 
sands in the winged Insects). They are never placed on 
movable pillars as the Lobster’s. Besides these, there are 
three simple eyes, called ocell?. The mouth may be fit- 
ted for biting (masticatory), as in Beetles, or for sucking 
(suctorial), as in Butterflies. The masticatory type, which 
is the more complete, and of which the other is but a mod- 
ification, consists of four horny jaws (mandibles and max- 
