232 CHILDHOOD OF ANIMALS 



living matter displays. To analyse them into their constituent 

 parts is a kind of vital chemistry still beyond our power, and it is still 

 more difficult to understand the complex results, arising from their 

 combinations in different proportions, than it is for us to understand 

 how it is that when hydrogen and oxygen are combined in a particu- 

 lar proportion, the qualities of the resulting water are so different 

 from the qualities of the two elements. Still less do we understand, 

 although we know that it must exist, the physical machinery by 

 which these complex inborn instincts are worked and transmitted 

 from parent to offspring. 



A few examples of some of the simpler elements out of which the 

 instincts are combined may make this difficult subject clearer. 

 They are what are known as tropisms, tendencies to turn towards, 

 or to turn away from, the source of physical stimulation, and are 

 found in all kinds of living matter, animal or vegetable. They 

 may be traced upwards to the most highly developed of living 

 beings, including ourselves, although in these latter they may be 

 disguised or controlled by the higher nerve-centres. The reaction 

 to light is known as phototropism or phototaxis. Many free-living 

 cells, especially the swarm-spores of plants, diatoms, and even 

 many colourless animal and vegetable organisms move in the direc- 

 tion of illumination, if the light be not too strong, but on over- 

 stimulation may move away from it. Other small organisms 

 move away from light towards darkness under all circumstances. 

 In some of the compound organisms this reaction to light, positive 

 or negative, may be shown by the direction of growth rather than 

 of locomotion, as when the shoot of a plant bends towards the light, 

 or its rootlet on emergence from the seed-capsule bends away from 

 it, and some of the plant-like compound polyps show precisely 

 similar reactions. Hydra bends towards light, some small worms 

 move towards it and others away from it. From these simple 

 reactions, we pass by easy transitions to the much more complicated 

 and yet more precise actions of the higher animals with eyes and 

 with definite nervous systems. Turn up a stone on the seashore 

 or a log of wood in a garden, and you will see numberless little 

 creatures disturbed by their exposure to light and at once setting 

 about wriggling, creeping or running, until they can get to darkness 

 again. The reaction begins before there is any trace of a definite 

 mechanism to produce it, and is continued up to those animals to 

 which even persons least inclined to assent to the existence of con- 

 sciousness in all living matter are quite ready to attribute some 



