A STUDY IN POLARITY 163 
decidedly unequal in length, the regenerated worm retains its 
old polarity. This is true whether the anterior or posterior cut 
edge is the longer, and has occurred in specimens where the ratio 
of the lengths of the cut edges was as lowas 9:7. The number of 
cases in which the anterior edge was the longer was, in Series I, 
5, in Series II, 2; in which the posterior side was the longer, 
Series I, 7, Series II, 5. 
ch g 
Fig. 5 Stages of regeneration of a triangular piece of worm cut so as to fulfill 
the conditions for Group D; a, showing the region from which the piece was 
taken; b, 1 day after operation; c, 2 days; d, 3 days; e, 5 days; f, 7 days; g, 10 days. 
D. If, when the vertex lies at or near the old median exis, 
and the angle at the vertex is 90° or less, the cut edges are equal 
in length, then the piece regenerates a head which is at right 
angles to the original median axis (figs. 5 to 10); if a pharynx 
develops, which very rarely happens (two cases only), this organ 
appears between the eyes and points toward the tip of the new 
head (fig. 7e, 9). The number of cases illustrating Group D was, 
in Series I, 15, in Series II, 5. In the regeneration of all other 
types of triangular pieces, the size of the piece influences the 
