130 THE GROUNDWORK OF SCIENCE

which external envelope each caterpillar makes its own

special cocoon, but which are so skilfully arranged as to

leave passages between them to facilitate their departure

when, as moths, the time has come for them to fly away.

The caterpillar of the emperor moth is described as

spinning for itself a double cocoon, but leaving an opening

fortified with elastic bristles pointing outwards, and so

directed that while they readily yield to pressure from

within, they firmly resist pressure from without. Thus the

caterpillar is at the same time both protected from intrusion

from outside, and enabled easily to obtain its own exit when

fully developed.

As an example of the blindness which characterises these

instinctive actions, we may refer to a kind of wasp which

does not enclose living food with her eggs, but from time

to time feeds the grubs which thence emerge with fresh

food, visiting her nest for that purpose at suitable intervals.

She covers her nest so carefully with sand that it is com-

pletely hidden, and this covering is replaced with equal care

after each of her visits. While it remains thus hidden she,

it is said, can always find it ; but if an entrance is made

ready for her, this, instead of helping her to get to her young,

seems to puzzle her completely, and even to prevent her

recognizing her own offspring.

But, as everyone knows, moths and butterflies habitually

lay their eggs on the leaves of such plants as will form

suitable food for the grubs when hatched, although the

parents themselves neither feed on such leaves nor make any

other use of them than that of serving as a receptacle for

their eggs. It may be that the parents are insects which, in

the adult condition, do not feed at all, and it is incredible

that they foresee the use to their unhatched young of leaves

useless to themselves, and the past utility of which to the

grubs they once were, they cannot be supposed to remember.

which external envelope each caterpillar makes its own

special cocoon, but which are so skilfully arranged as to

leave passages between them to facilitate their departure

when, as moths, the time has come for them to fly away.

The caterpillar of the emperor moth is described as

spinning for itself a double cocoon, but leaving an opening

fortified with elastic bristles pointing outwards, and so

directed that while they readily yield to pressure from

within, they firmly resist pressure from without. Thus the

caterpillar is at the same time both protected from intrusion

from outside, and enabled easily to obtain its own exit when

fully developed.

As an example of the blindness which characterises these

instinctive actions, we may refer to a kind of wasp which

does not enclose living food with her eggs, but from time

to time feeds the grubs which thence emerge with fresh

food, visiting her nest for that purpose at suitable intervals.

She covers her nest so carefully with sand that it is com-

pletely hidden, and this covering is replaced with equal care

after each of her visits. While it remains thus hidden she,

it is said, can always find it ; but if an entrance is made

ready for her, this, instead of helping her to get to her young,

seems to puzzle her completely, and even to prevent her

recognizing her own offspring.

But, as everyone knows, moths and butterflies habitually

lay their eggs on the leaves of such plants as will form

suitable food for the grubs when hatched, although the

parents themselves neither feed on such leaves nor make any

other use of them than that of serving as a receptacle for

their eggs. It may be that the parents are insects which, in

the adult condition, do not feed at all, and it is incredible

that they foresee the use to their unhatched young of leaves

useless to themselves, and the past utility of which to the

grubs they once were, they cannot be supposed to remember.