the silverfish, are of primitive design, appearing in the Devonian.
Thysanura is thought by some to be the linking order between wingless
and winged insects. The compound eyes are small; have three tail
bristles on the end of their abdomen; the mouthparts are external;
some species have scales covering the body. After hatching, the
nymphs change to adults with minimal metamorphosis. The young
are similar to adults except in size, molting until sexual maturity
is attained. Molting may continue into adulthood, and there may
be more than forty molts in the life of a thysanuran. There are
some 700 named species.