124 THE ORIGIN OF THE NERVOUS SYSTEM 



so far as can be determined. The single or biaxial 

 planarian heads may contain fully developed cephalic 



23 29 



FIGS. 23-29. Tubularia: Fig. 23, an unbranched individual; 

 Figs. 24-29, single and biaxial apical structures which develop from 

 short pieces of the stem (from Child, 



ganglia. In such cases there can be no doubt that 

 these apical or cephalic structures have arisen in com- 

 plete independence of other parts of the body. Thus 



