276 
HALF HOURS WITH INSECTS. [Packard. 
extinctions and creations of new faunas out of preceding 
ones, as are indulged in by naturalists of the present day, in 
the light of the knowledge pouring in upon them from Arctic 
explorers and western geologists ? Granted these extraordi¬ 
nary changes in the ph} 7 sical surroundings of the animals 
whose descendants people our land, do not a host of ques¬ 
tions arise as to the result in the beings of our day of these 
changes in the modes of life, the modes of thought, so to 
speak, the formation of peculiar instincts arising from new 
exigencies of life, which have remodelled the whole psychol¬ 
ogy, as it were, of the animals of our country? Instincts 
vary with the varying structure and form of the animals. 
Change the surroundings, and at once the mode of life and 
psychology of the organism begin to undergo a revolution. 
These changes may result in the gradual extinction of whole 
assemblages of animals, which are as gradually replaced by 
new faunas. 
Many, indeed most, insects are in our northern hemisphere 
represented in the colder months of the year by the chrysa¬ 
lis or eggs. These are eagerly sought after by the smaller 
birds, and are in most cases protected by their colors, or by 
their resemblance to the bark of the trees on which they 
may be laid. The eggs of the canker worm are gray, like 
the bark of the tree or paling on which they are deposited. 
The eggs of the tent caterpillar are covered over with a 
coating of gum, so that the bunch looks like an excrescence 
on the tree. The chrysalis of Vanessa Antiopa is exactly 
of the color of old wood, and it is often found hanging from 
fences and out-houses, while, before houses were built, for 
this butterfly belongs to an ancient family, it assimilated in 
hue the bark of trees. The cocoons of many of the silk 
moths, like those of the Promethea moth, are covered with 
leaves drawn around them in the process of weaving, and 
hang all winter on the wild cherry, having the semblance of 
a dead leaf. Those of the Polyphemus (Fig. 214) which fall 
20 
