HEAD-FREQUENCY IN PLANARIA 



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pieces, being often used as a class experiment, and always with 

 the same result, a higher head-frequency in the pieces from 

 larger animals. 



It may appear at first glance that these differences in head- 

 frequency are due simply to the fact that in the longer older 

 animals and the pieces of larger size there is more available 



TABLE 1 

 Head-frequency in relation to physiological age {size) 



nutritive material for the development of a new head, but 

 there are various reasons for believing that this is not the case : 

 first, head-frequency is lowest in pieces from levels near the 

 mouth where the amount of nutritive material in the pieces is 

 greatest; second, it has been shown elsewhere that head-fre- 

 quency may be altered experimentally in both directions with- 

 out altering the amount of nutritive material (Child, '16; Behre, 



