CONTROL OF HEAD-FORM IN PLANARIA 



111 



upward shift in c than the short period. The effect of twenty- 

 four hours in KCN m/200000, as shown in II a-c of this series 

 is essentially similar to the effect of the same concentration for 

 the same time in table 1, II a-c. 



In series 432, table 5, the effect of thirteen days in two con- 

 centrations m/100000 (II a-c) and m/200000 (III) is shown. 

 In both concentrations there is a very great shift downward in 

 the a-pieces, a slight shift downward in the h pieces, more marked 

 in the higher concentration, II h, than in the lower, III h, while 



TABLE 5 



Series 4^2. Wor77is 16-18 mm., in laboratory twenty-six days before experitnent: 

 I. Control in water; II. KCN m/100000 thirteen days with reneival every forty- 

 eight hours; III. KCN m/200000 thirteen days with renewal every forty-eight hours 



in c there is a very marked shift upward, slightly greater in the 

 lower concentration. III c, than in the higher II c. This upward 

 shift in head-frequency in the c-pieces, however, does not in- 

 crease the frequency of normal heads but merely shifts the head- 

 frequency toward the normal end of the series. 



This period of thirteen days in KCN is sufficiently long so 

 that very few or no changes in character of the heads occur 

 after the pieces are returned to water. Since this is the case, 

 this series may be compared in certain respects with Series 489, 

 table 3, and with III, a-c of Series 457, table 4, where the pieces 

 Avere kept in cyanide during the whole period of reconstitution. 

 In general the results are similar in all; a marked shift downward 

 in a, a slight effect in h and a shift upward but with little or no 



