THE PURPOSE OF YOUTH 



227 



there are continuous fibres from the cells in the brain to the remotest 

 tissues of the body. Other fibres are continued to the web-fibres 

 of other brain-spiders. The sys- 

 tem might be compared with a 

 very complicated set of telephone 

 exchanges, each exchange supply- 

 ing a certain district near at hand 

 or far away, and each linked up 

 with a number of other exchanges 

 with their districts. The greater 

 the number of subscribers' wires 

 to each exchange and the greater 

 the number of connections with 

 other exchanges, the more perfect 

 the system would be. 



The details of the development 

 of the brain are difficult and 

 obscure, but there is a good deal 

 of evidence to show that the actual 

 number of brain-cells does not 



increase during childhood, youth, 



or adult life. The initial number 



of cells may be taken as an index 



or physical correlate of the natural 



endowment. Species or indi- 

 viduals with many of them 



in a given area have a richer 



potentiality of mental life. 



In the new-born mammal, 



however, large numbers of 



the brain-cells lie isolated 



and quiescent in the grey 



matter ; they are joined up 



neither to each other nor to 



distant parts of the body. 



In early infancy the brain 



has little or no control over 



even the chief muscles and FIG. 36. Brains of Primates. The largest 



f ,, , , . . (lowest figure) is human; next, that of 



tissues OI the body* 1 ills IS a chimpanzee; next, that of a macaque 



probably the explanation of monkey; next (uppermost figure), that 



r J . of a cebus monkey. (The figures are all 



a famous observation much reduced to the sarne scale. ) 



