THE PURPOSE OF YOUTH 233 



form of consciousness. Very low in the series, too, we see the 

 simple reaction changing with the state of the creature to which 

 it is applied, the turning towards light, for instance, being reversed 

 to a turning away from it, when the stimulation reaches a certain 

 degree of intensity. And so long before the dawn of consciousness, 

 unless the term consciousness be so attenuated as to be meaningless, 

 we get a beginning of adaptive response. 



The contact tropisms are other factors of instinct at first extremely 

 simple. A free-swimming, single-celled creature, animal or plant, 

 which comes in contact with an obstacle, responds in some way. 

 It may shrink back, sometimes with a little turning movement, 

 and advance again, and ft may proceed by this system of trial and 

 error until it finds a way round. On the other hand, if an amoeba 

 come across a solid surface, it at once creeps out over it, for it is 

 the habit of that creature to creep in contact with any flattened 

 surface, instead of drifting freely in the mud or water. A growing 

 rootlet burrows into every crevice, whilst a shoot moves in the 

 direction of free space and air. As we ascend the scale of the 

 animal kingdom, we find numberless creatures, low and high, 

 which exhibit such a choice with regard to surfaces. The stems 

 of polyps grown in a glass tank cling closely to the walls of the 

 vessel, but their upper portions, carrying the mouth and tentacles, 

 turn outwards towards the open space. Free-swimming larvae 

 wriggle out of a crevice if they drift into it. Most marine worms 

 move about restlessly until they have an opportunity of burrowing 

 into sand, or of creeping into some chink in the rocks. A very 

 large number of insects, from cockroaches to ants, and whether 

 they are exposed to light or kept in the dark, will move about rest- 

 lessly until they can squeeze between the folds of a sheet of paper, 

 or into some similar place where they are in contact with a surface 

 all round. In an aquarium, pieces of drain-pipe have to be placed 

 for many different kinds of fish, such as eels and pike, whilst others 

 become restless if they are enclosed in such a fashion. So also 

 amongst reptiles, there are some which must be provided with 

 retreats into which they can creep, others which like to lie in the 

 open. Amongst mammals there are some that cannot be persuaded 

 to enter any box or chamber if it appear to be closed. Deer, 

 antelopes, cattle and sheep and most of the large carnivores can 

 be boxed only with the greatest trouble, sometimes by the device 

 of making the box apparently a narrow tunnel open at the end 

 turned away from the entrance. Such animals often damage 



