94 
INTRODUCTION. 
ing to black. Occasionally, liowoTcr, they are of 
brighter hues ; that of Geomctra alniaria is bluish ; 
that of the dark crimson, underlying (' Catocala 
sponsa J, lilac ; ;md that of the common Magpie- 
moth C Abraxas ffrossulariata J, a species remarkable 
for the similarity of its colours through all its diffe- 
rent stages, is ornamented with alternate rings of 
black and yellow. 
The security which arises to the pupae of butter- 
flies from being hun^/ out of the way of danger, is 
provided for among moths, by enveloping them in 
a dense tissue of silk or extraneous substances, and 
frequently by burying them in the earth or in the 
interior of plants. This covering of the clnysalis, 
of whatsoever materials it is composed, is named the 
cocoon. Silk is almost always used in its composi- 
tion, and in very many cases it is the only substance 
employed. Li structure, texture, .and many other 
liroperties, cocoons vary extremely. Sometimes the 
caterpillars content themselves with filling a certain 
space with threads, crossing each other in various 
directions, and leaving many voids between them : 
in the centre of this loose web the chrj'salis is placed. 
In other instances the fabric is more closely woven, 
but still sufficiently open to allow the chrysalis to 
be seen, and apparently inadequate to protect it 
from the weather. In such cases, however, addi- 
tional shelter is often obtained by drawing round 
it a few of the leaves among which it is usually 
placed. Many hairy larvm increase the compactness 
of their cocoons by stripping their own bodies and 
