o show some traces of the division of labour (and modification
of structure) which make the bees so interesting; but in this case the
living bees, rising from a solitary life through increasing stages of
social co-operation, give us some idea of the gradual development of
this remarkable citizenship.

It seems to me that the great selective agency which has brought about
these, and many other remarkable activities of the insects (such as the
storing of food with their eggs by wasps), was probably the occurrence
of periods of cold, and especially the beginning of a winter season in
the Cretaceous or Tertiary age. In the periods of luxuriant life (the
Carboniferous, the Jurassic, or the Oligocene), when insects swarmed and
varied in every direction, some would vary in the direction of a more
effective placing of the eggs; and the supervening period of cold and
scarcity would favour them. When a regular winter season set in, this
tendency would be enormously increased. It is a parallel case to the
evolution of the birds and mammals from the reptiles. Those that varied
most in the direction of care for the egg and the young would have the
largest share in the next generation. When we further reflect that since
the Tertiary the insect world has passed through the drastic disturbance
of the climate in the great Ice-Age, we seem to have an illuminating
clue to one of the most remarkable features of higher insect life.

The origin of the colour marks' and patterns on so many of the higher
insects, with which we may join the origin of the stick-insects,
leaf-insects, etc., is a subject of lively controversy in science
to-day. The protective value of the appearance of insects which
look almost exactly like dried twigs or decaying leaves, and of an
arrangement of the colours of the wings of butterflies which makes them
almost invisible when at rest, is so obvious that natural selection was
confidently invoked to explain them. In other cases certain colours
or marks seemed to have a value as "warning colours," advertising the
nauseousness of their possessors to the bird, which had learned to
recognise them; in other cases these colours and marks seemed to be
borrowed by palatable species, whose unconscious "mimicry" led to their
survival; in other cases, again, the patterns and spots were regarded as
"recognition marks," by which the male could find his mate.

Science is just now passing through a phase of acute criticism--as
the