CHAPTER XIV. 
THE ANOPLURA — THE THYSANURA. 
THESE are the most degraded forms of insects, and they never 
obtain, during any time of their lives, those elaborate structures 
which are usually considered to be characteristic of the class. 
The members of the species of Anoplura and Thysanura are 
invariably wingless, and their young are hatched almost as fully 
developed as the adults. They do not undergo metamorphosis, 
but their growth and development are accompanied by the phe- 
nomena of skin changing. 
It appears that when the parasitic lice or Pediculi — which consti- 
tute an important portion of the class Anoplura — are hatched from 
the egg, they have not much subsequent alteration to submit to, as 
they are nearly perfect. Moreover, the young louse is not more 
perfect than the adult, and, therefore, no retrograde metamorphosis 
takes place. The caterpillars of Psyche and Orgyia turn either into 
male moths with beautiful wings or into females with the most 
rudimentary organs of flight, and this occurs because these last 
submit to a retrograde metamorphosis. The adult female Orgyia 
is absolutely lower in organisation than the caterpillar. But, 
although there is some resemblance between these female moths 
and the Anoplura , it must be remembered that the lice retain 
their larval condition through life. There are some proofs, how- 
ever, that there is a retrograde development in the louse before 
it is hatched. Until late in its life within the egg the louse grows, 
and is formed like the embryos of other insects, and then, just 
before hatching, takes on its peculiar degraded aspect and essential 
