PHYSIOLOGY OF RECONSTITUTION OF PLANARIA LATA. 



135 



been found that head frequencies may be altered in opposite direc- 

 tions in pieces from different levels of the same animals by the 



3 -- 



2 - 



1 - 



Fig. 23. Head frequencies of fourths and sixths in old and young individu- 

 als of P. lata: fourths, young, unbroken line; sixths, young, dotted line; 

 fourths, old, long dashes; sixths, old, dots and dashes. The curves in this 

 graph are taken from Figs. 21 and 22. 



same concentration of a single agent (Child, '16; Buchanan, '22). 

 In pieces which normally show a high head frequency it may be 

 decreased and in pieces which normally show a low head frequency 



