MONITORS 229 



same principles are in use all around us by other animals. 

 Whatever the truth may be it is certain that no animals 

 navigate consciously on their migrations. In the first place 

 it is highly improbable that an animal can have any sort of 

 mental chart or picture of the geography of the globe or, 

 secondly, that it knows where it is in relation to distant 

 places. It is probable that it finds itself travelling in a certain 

 direction with no more realization of what it is doing than 

 a man on a bicycle has when he turns a corner — he just goes 

 round without conscious effort. When, however, the animal 

 finds itself in surroundings that it has inhabited before, its 

 memory of local landmarks and former habit will lead it to 

 its exact destination ; but that, of course, is not navigation. 

 Throughout these chapters we have seen that animals, 

 from the simplest to the most complex, are endowed with 

 sense-organs that enable them to adapt their behaviour to 

 the nature of their surroundings. Animals are as it were shut 

 up in their own bodies and are desperately trying to find 

 out what is going on outside. The simpler senses tell them 

 something about the objects with which they come in contact, 

 the more complicated ones about things which are at a 

 distance. Equally important are the senses that tell what is 

 happening inside the body. The sum of the information 

 supplied by the senses is used for the two primary purposes 

 of life, if we may speak teleologically, or assume that it has 

 purpose — staying alive by finding food and avoiding dangers, 

 and reproducing by finding a mate and leaving progeny to 

 fill the gap that will be left at the final error in interpreting 

 the messages from the sense organs, or at a misfortune against 

 which they give no protection. All the more complex 

 sense-organs are, in effect, transformers for turning stimuli 

 of all kinds into physico-chemical changes at the nerve- 

 endings. The changes start impulses travelling along the 

 nerves and they are relayed either by the central nervous 

 system or by shorter paths to the muscles and other structures 

 that can make the appropriate response. Apart from the 

 shorter reflex paths, the senses are of no avail without the 

 brain to interpret and co-ordinate the messages received 

 from the end-organs. In spite of all the beautiful mechanisms, 

 the brain can easily be mistaken in its interpretation, 



