A STUDY IN POLARITY 165 
“Although the amount of old tissue at the anterior end is rel- 
atively little, yet the growth of the new material that forms in 
this region is greater than that of the material at the side im- 
mediately behind the head and along the side of the piece. More 
material is formed where the head is to appear than behind that 
region.”” He thinks it probable that this is due to greater cell 
growth at the anterior end rather than to a migration of cells 
into this region. 
eS fy 
e 
d 
Fig. 7 Case similar to that of figure 5; b, after 3 days; c, 5 days; d, 9 days; 
e, 19 days. 
One could suppose from an examination of many of the pieces 
in the earlier stages of regeneration (figs. 5d, 6b, 7b) that a new 
head would be formed along the anterior, and a tail along the 
posterior edge, just as in the case of pieces which are cut obliquely, 
since the accumulations of material at the centers of the anterior 
and posterior edges are so distinct from each other. This, how- 
ever, does not take place. The indentation which often marks 
the boundary between anterior and posterior accumulations 
of new material becomes less and less pronounced until it is 
