NERVOUS SYSTEM AND OTHER PARTS 



125 



far no other region of the body has ever been seen to 

 develop from pieces in this way. All other levels of 

 the body along the polar axis develop only in relation 

 to more apical or more anterior regions. In Planaria, 

 for example, we never find small pieces transforming 

 completely into a new posterior end, although pieces may 



o c 



3° 





Figs. 30-36. — Partial structures from short pieces of Planaria: 

 Figs. 30-33, monaxial and biaxial heads from P. dorotocephala; Fig. 34, 

 biaxial heads from P. simplicissima; Fig. 35, biaxial tail from P. doroto- 

 cephala; Fig. 36, biaxial tail from P. simplicissima (Figs. 30-33, 35, 

 from Child, 1915c). 



give rise to new posterior ends on one (Figs. 11-12) or on 

 both cut surfaces (Figs. 35-36) in the absence of a head. 



THE RELATIVE INDEPENDENCE OF THE NERVOUS SYSTEM 



IN DEVELOPMENT 



All the data both from normal ontogeny and from 

 experimental or regulatory reproduction indicate that 

 the apical region or head, at least as regards the earlier 



