354 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



in 21 per cent. The few forms listed as apolar in Table 9 are without 

 either head or tail, and those Hsted as bipolar are bipolar heads. Percen- 

 tages of deaths in the different lots do not differ sufficiently to affect the 

 general result. With increase in frequency of posterior development after 



TABLE 9 



ALTERATION OF SCALE OF ORGANIZATION IN Dugesia PIECES BY EXPOSURE TO KCN 



m/lOO,000 FOR 72 HOURS FOLLOWING SECTION (lOO PIECES IN EACH LOT) 



(Data from Rulon and Child, 193 yi) 



TABLE 10 



Differential Inhibition of Head Development in Those Pieces 



OF Table 9 Which Develop Pharynx and Tail* 



(Data from Rulon and Child, 19376) 



*For the characteristics of the diEEerentially inhibited heads see pp. 177-80. 



KCN there is also increase in frequency of differential inhibition of head 

 development, as shown in Table lo. That inhibition of head development 

 decreases scale of organization in long posterior pieces was shown by the 

 experiments described above. Table lo gives additional, though some- 

 what less direct, evidence of the same relation between head develop- 

 ment and scale of organization in these short anterior pieces. 



