92 EVOLUTION 



and in its consequences, which include our 

 knowing our right hand from our left. 



Ttisjikgly that certain " worms " were the 

 first. aniTpals df^fiTiite]y t.Q abandon the jnnre 

 prirrHljye rft.rh'fll syrnfn^try., to begin moving 

 with one part of the body always in front, to 

 acquire head and sides. And if one end of 

 the body constantly experienced the first 



it seems 



reasonable to suppose that sensitive and ner- 

 vous cells would be most developed in that 

 much-stimulated, and otherwise over-edu- 

 cated, jiead regjofl- But a brain always 

 arises from tfrg r s)nfaing in of fptodpnmV pp11 



j and its be- 



ginning in the cerebral ganglion of the sim- 

 plest "worms" is thus in part explained. 

 It is difficult to over-estimate the importance 

 of the establishment of an anterior brajii - 

 motor and sensory and co-ordinating 

 an d the consequent evolution 



of a head. 



THE BEGINNINGS OF BEHAVIOUR. Jen- 

 nings has shown that some <i janiceIh^Ija l r.,A3ij- 

 mals "behave " in a very definite way. They 

 are rtgt me^ Q 1 1 f ^^ g -* a which rush about as 

 long as their spring keeps unrolling, and they 

 are more than the merp slaves of st.mpj1iis-_ 

 There are some, it is true, which seem to 

 have only one kind of reaction to every kind 



