PHYSIOLOGICAL GRADIENTS 



IOI 



u 



a 



- \ 

 ■ 



12 



Figs. 8-12. — Reorganization in pieces from different body levels, 

 a and b, in relation to presence or absence of a head; Planaria doroto- 

 cephala: Fig. 8, diagrammatic outline, indicating levels from which 

 pieces are taken; Fig. 9, normal animal developing from cither a or b 

 when head arises; Fig. 10, anophthalmic form with rudimentary head, 

 but developing all parts of body, whether taken from a or !>; Fig. 11, 

 headless form from region a, develops all parts posterior, but none 

 anterior to region a, from which it was taken; Fig. 12, headless form 

 from region b, develops all parts posterior, but none anterior to its own 

 level (from Child, 1915c). 



