digestive and reproductive systems. In this part of the body the
skeletal ring of each segment is joined to that of the segments
before and behind it in the same manner. But in other parts of the
body we shall find the skeletal pieces of each segment and the rings
of successive segments fused in one plate of mail. The legs are the
parapodia of annelids carried to a vastly higher development. They
are slender and jointed, and yet often very powerful. A large
portion of the muscular system of the body is attached to these
appendages.

But the insect has also jaws. The annelid had teeth or claws
attached to the proboscis. But true jaws are something quite
different. They always develop by modifying some other organ. In the
insect they are modified legs. This is shown first by their
embryonic development. But the king- or horseshoe-crab has still no
true jaws, but uses the upper joints of its legs for chewing. There
are primitively three pairs of jaws of various forms for the
different kinds of food of different species or higher groups. But
some of them may disappear and the others be greatly modified into
awls for piercing, or a tube for sucking honey. Into the wonderful
transformations of these modified legs we cannot enter.

The muscles are no longer arranged to form a sack as in annelids.
Transverse muscles, running parallel to the unyielding plates of
chitin or horn could accomplish nothing. They have largely
disappeared. The work of locomotion has been transferred from the
trunk to the legs.

The abdomen of the insect is as clearly composed of distinct
segments as the body of the annelid. Of these there are perhaps