FIGURE NO. 10 



EVOLUTION AND DEVELOPMENT OF 

 NERVE-CELLS 



(After Ramon y Cajal) 



A-D, nerve-cells or neurons from four Vertebrate 

 animals : — A, a fish, B, a reptile, C, a bird, D, a mam- 

 mal. The evolution is marked by increased complexity 

 in the branching of the nerve-fibres. But the figures 

 a-e show five stages in the individual development of 

 the neurons of a bird. The individual development re- 

 capitulates the racial evolution. 



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