170 J. M. D. OLMSTED 
results show that the worms with axes at right angles to the 
original axes are most often present when long narrow strips are 
cut from the side. Pieces of this kind show a marked tendency 
to become crescent shaped. . . . The new material is formed 
in the concavity of the crescent, and it is all used up in the 
d 
Fig. 12 Stages in the headless regeneration of a piece from right side of worm. 
a, 5 days after operation; b, 8 days; c, 14 days; d, 20 days; d was drawn while the 
piece was in chloretone, hence the protrusion of the pharynx. 
formation of the new head. There is no material left over for 
the formation of the other parts.’’ He adds, ‘‘This is not, of 
course, an explanation of the phenomenon, but it is only a 
restatement of the facts.’ Again he remarks in regard to cross- 
pieces (’01, p. 46). “Since the tendency to produce a head 
approaching the maximum size is stronger than the tendency 
to produce as much of the missing anterior end, all the new 
material goes into the new head.” 
