BARK - LICE. 
251 
threads, which are fastened, in a radiated manner, around 
their bodies, to the bark, and serve to confine them securely 
in their places. After becoming thus fixed they remain 
apparently inanimate ; but under these lifeless scales the 
transformation of the insect is conducted ; with this remark- 
able difference, that in a few days the large ones contrive 
to break up and throw off, in four or five flakes, their outer 
scaly coats, and reappear in a very similar form to that 
which they before had ; the smaller ones, on the contrary, 
continue under their outer skins, which serve instead of co- 
coons, and from which they seem to shrink and detach them- 
selves, and then become perfect pupa;, the rudiments of 
wings, antennae, feet, &c. being discoverable on raising the 
shells. 
If we follow the progress of these small lice, which are 
to produce the males, we shall see, in process of time, a pair 
of threads and the tips of the wings protruding beneath the 
shell at its lower elevated part, and through this little fissure 
the perfect insect at length backs out. After the larger lice 
have become fixed, and have thrown off their outer coats, 
they enter upon the pupa or chrysalis state, which continues 
for a longer or shorter period, according to the species. But 
when they have become mature, they do not leave the skins 
or shells covering their bodies, which continue flexible for 
a time. These larger insects are the females, and are des- 
tined to remain immovable, and never change their place 
after they have once become stationary. The male is ex- 
ceedingly small in comparison to the female, and is provided 
with only two wings, which are usually very large, and lie 
flatly on the top of the body. 
After the insects have paired, the body of the female 
increases in size, or becomes quite convex, for a time, and 
ever afterwards remains without alteration ; but serves to 
shelter the eggs which are to give birth to her future off- 
spring. These eggs, when matured, pass under the body 
of the mother, and the latter by degrees shrinks more and 
