INTRODUCTORY 7 



circumstances prove disadvantageous or even destructive instead 

 of beneficial, although the perfection of many of the adjustments 

 of Crustacea and insects is marvellous. Some hunting wasps 

 store living spiders in the cells with their eggs to serve as food 

 for their young, but each spider, while alive, is paralyzed and 

 helpless, for when the wasp captures it she stings it through the 

 nerve-centre which directs the movements of the limbs, severely 

 enough to produce paralysis without destroying life ; and Mivart 

 says ("Lessons from Nature," p. 202) that the female wasp does 

 this by nature or without experience. 



It is often said that the natural activities of living things are 

 innate ; but, so far as this word implies that they take place with- 

 out a stimulus, it is obviously erroneous. The hermit-crab is said 

 to seek a house by nature, and the egg to grow into a specific 

 organism in virtue of its inherent potency ; but this is not strictly 

 true, for while some vital changes may be spontaneous, in one of 

 the many meanings of this word, there is no reason to believe 

 that any change ever takes place, either in living things or any 

 where else, without antecedents which stand in that peculiar rela- 

 tion which we call physical causation. 



The new-born child is said to seek the breast instinctively, but 

 every nurse knows that it does not seek the breast at all without 

 experience, although it does suck by nature and without instruc- 

 tion the first time the nerves of its lips and tongue are stimulated 

 by contact with the nipple. The instinct of the young hermit-crab 

 cannot be called spontaneous, if, by this word, we mean arbitrary, 

 although it is so promptly called forth by the first sight of a shell. 



The bodily movements of which the purpose is most obvious 

 are, as a rule, called out in response to changes in the external 

 world, and they are excited by stimuli which come through the 

 senses ; although many responsive actions are called forth by 

 stimuli which arise within the body and do not reach it through 

 any of the organs of special sense, as the stretching of our limbs 

 while awakening is excited by the vague discomfort of the body; 

 and this is true not only of many bodily movements but of most 

 physiological changes. 



"To call mind a function of the brain," says Maudsley ("Re- 

 sponsibility in Mental Disease," p. 17), "may lead to much mis- 



