A STUDY IN POLARITY 159 
were in the contracted state. The drawings made while the 
pieces were still in chloretone formed the basis for classification 
into groups, according to the relative lengths of the cut edges, 
the size of the angle at the vertex, etcetera. The drawings 
made on the day after the operation during the earlier experi- 
ments were compared with those of the later work and each of 
the earlier ones was placed in that group which it most resembled. 
One may fairly assume that pieces which resemble one another 
on the day after operation would also have been similar immedi- 
ately after the operation. Thus it was possible to estimate with 
some degree of accuracy the measurements which the triangular 
pieces in the earlier work had immediately after operation. 
In the following account it was thought best, however, to enumer- 
ate the cases separately; hence the earlier experiments, in which 
the original measurements are estimated merely, are referred to 
as Series I, whereas the later ones, in which the pieces were 
drawn while still in chloretone, are designated as Series II. 
The mortality of such triangular pieces is very great. Less 
than one-fifth of them survive the operation and regenerate. 
Pieces taken from the region of the pharynx (fig. 5a) had the 
greatest vitality, though regeneration of pieces from other regions 
of the body, if accomplished, proceeded along exactly the same 
lines as in the pieces from near the pharynx. Bardeen (03) 
found that in Planaria maculata he could more frequently obtain 
double-headed worms from cross-pieces when they were taken 
from the pharyngeal region than when from any other region 
of the body. Morgan (’04) was also more successful in getting 
pieces from this same region to regenerate, but he remarks, 
“Whether this is only because shorter pieces are more easily 
obtained here, or because the very short pieces from this region 
survive the operation, remains an open question.” The latter 
explanation seems to be the true one, since in many cases in my 
experiments the same sized pieces were taken from all regions 
of the body and only those from near the pharynx survived. 
When, in the operation of cutting, the epidermal layer -is 
broken, a great mass of loose parenchyma cells flows out from 
the wound, and if the two cuts form a very acute angle, the 
