A STUDY IN POLARITY 75 
These expressions of the tendency of all triangular pieces to 
retain their original polarity, together with the fact that slight 
deviations from certain definite positions of the cuts always 
result in complete failure to displace the original polarity, lead 
one to suspect that, even in those cases in which the head ap- 
pears to be at right angles to the original long axis, the original 
polarity has not been fundamentally changed. 
SUMMARY 
1. Triangular pieces cut from the side of Planaria maculata, 
as in figure 2a, regenerate heads at right angles to the original 
long axis of the worm from which they were taken only when the 
following conditions are fulfilled: (a) the point of the inter- 
section of the two cut edges must lie at or near the old median 
axis of the worm; (b) the angle between the cut edges must be 
90° or less; (ec) the cut edges must be of the same length. 
2. Under all other conditions the original polarity is most 
evidently unchanged. If the piece is small, it may regenerate 
a head only, but the position of this head shows the tendency to 
retain the old polarity. 
3. In triangular pieces whose heads are at right angles to the 
original long axis the first eye to appear is the one which les 
nearer the anterior end of the uncut edge. 
4. The nervous system of such a regenerated triangular piece 
is an unbroken ring. 
5. If a pharynx is developed, it appears between the eyes 
and points toward the tip of the new head. 
6. A head-bearing piece of Planaria maculata whose geomet- 
rical long axis, artificially established, does not coincide with its 
original morphological axis, will not retain the form in which 
it was cut, but regenerates with its original polarity unchanged. 
7. All the data of these experiments point to the possibility 
that polarity, even in the most extreme cases, has not been 
fundamentally changed. 
