EXPLANATORY HYPOTHESES 117 



forefathers. The migratory instinct in the young 

 salmon has prevented its being naturalised in New 

 Zealand and Tasmania. Thousands of ova have 

 been hatched, and the young fish have been seen at 

 the mouths of the rivers before they went to siea ; 

 but none are known to have returned. They have 

 wandered away in the direction that their parents 

 were accustomed to take, and they have lost them- 

 selves. But plants also have instincts which 

 cannot be due to imitation. Eoots grow downwards 

 and stems grow upwards by instinct. It is instinct 

 which makes the ivy grow towards the shade and 

 the clematis towards the light. These examples 

 are quite sufficient to prove that habits are trans- 

 mitted. Imitation may be a help in the early 

 stages of a habit, but it is not necessary. 



Next, as to the question of the existence of mind 

 in 'each cell, it has been known for a long time that 

 irritability is one of the qualities of living proto- 

 plasm. No one can watch the movements of in- 

 fusorians, even for half-an-hour, without recog- 

 nising mental action. Also an amoeba surrounding 

 another organism and feeding upon it is as much a 

 proof of mental action as a cat catching a mouse. 

 The search for the ovum by the spermatozoid is also 

 a mental action ; even if it is led in its search by 

 physical agents. A very remarkable example is 

 those Ehizopods like Diffulgia and Saccammina 

 which build up cases of grains of sand. They atfe 

 born naked, and from the sand in which they are 

 born they select particles of about equal size, and 

 build them up into a protective shell. Some select 



