CONTROL OF HEAD-FORM IN PLANARIA 



109 



and when they are placed in it about an hour after section (HI). 

 The shift in head-frequency downward as compared ^^ith the 

 control is greater in II a than in III a; in h there is no marked 



change in either direction, while in both II c and III c there is 

 a very great shift upward as compared with the control. 



Series 457, table 4, is a comparison of the effect of twenty- 

 four hours (II) and twenty days (III), i.e., the whole period of 

 reconstitution in a given concentration of cyanide. In II the 

 cyanide for twenty-four hours is without effect in shifting the 



