The Opossums are mainly arboreal marsupials, insectivorous and
carnivorous, confined to the American Continent from the United States
to Patagonia. Many have no pouch and carry their numerous young ones on
their back, the tail of the young twined round that of the mother. The
opossums are agile, clever creatures, and famous for "playing 'possum,"
lying inert just as if they were dead.]
[Illustration: MALE OF THREE-SPINED STICKLEBACK, MAKING A NEST OF
WATER-WEED, GLUED TOGETHER BY VISCID THREADS SECRETED FROM THE KIDNEYS
AT THE BREEDING SEASON]
[Illustration: A FEMALE STICKLEBACK ENTERS THE NEST WHICH THE MALE HAS
MADE, LAYS THE EGGS INSIDE, AND THEN DEPARTS
In many cases two or three females use the same nest, the stickleback
being polygamous. Above the nest the male, who mounts guard, is seen
driving away an intruder.]
When we draw back our finger from something very hot, or shut our eye to
avoid a blow from a rebounding branch, we do not will the action; and
this is more or less the case, probably, when a young mammal sucks its
mother for the first time. Some Mound-birds of Celebes lay their eggs in
warm volcanic ash by the shore of the sea, others in a great mass of
fermenting vegetation; it is inborn in the newly hatched bird to
struggle out as quickly as it can from such a strange nest, else it will
suffocate. If it stops struggling too soon, it perishes, for it seems
that the trigger of the instinct cannot be pulled twice. Similarly, when
the eggs of the turtle, that have been laid in the sand of the shore,
hatch out, the young ones make _instinctively_ for the sea. Some of the
crocodiles bury their eggs two feet or so below the surface among sand
and decaying vegetation--an awkward situation for a birthplace. When the
young crocodile is ready to break out of the egg-shell, just as a chick
does at the end of the three weeks of brooding, it utters
_instinctively_ a piping cry. On hearing this, the watchful mother digs
away the heavy blankets, otherwise the young crocodile would be buried
alive at birth. Now there is no warrant for believing that the young
Mound-birds, young crocodiles, and young turtles have an intelligent
appreciation of what they do when they are hatched. They act
instinctively, "as to the manner born." But this is not to say that
their activity is not backed by endeavour or even suffused with a
certain amount of awareness. Of course, it is necessarily difficult for
man, who is so much a creature of intelligence, to get even an inkling
of the mental side of instinctive behaviour.
In many of the higher reaches of animal instinct, as in courtship or
nest-building, in hunting or preparing the food, it looks as if the
starting of the routine activity also "rang up" the higher centres of
the brain and put the intelligence on the _qui vive_, ready to interpose
when needed. So the twofold caution is this: (1) We must not depreciate
the creature too much if, in unusual circumstances, it acts in an
ineffective way along lines of behaviour which are normally handed over
to instinct; and (2) we must leave open the possibility that even
routine instinctive behaviour may be suffused with awareness and backed
by endeavour.
§ 2