PHYSIOLOGY OF RECONSTITUTION OF PLANARIA LATA. 131 



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Fig. 21. Head frequencies in relation to length of piece and level of body. 

 P. lata: fourths, unbroken line, no animals; sixths, long dashes, 250 animals; 

 eighths, short dashes, 850 animals; sixteenths, alternating long and short 

 dashes, 100 animals. P. dorotocephala: fourths, dotted line, no animals; 

 sixths, alternating dots and long dashes, no animals; eighths, alternating 

 dots and short dashes, 70 animals ; sixteenths, two dots alternating with short 

 dashes, 60 animals. On the outline of P. lata below the graph the levels of 

 section of pieces of different length are indicated : A—D, large capitals, 

 fourths ; A-F, small capitals, sixths ; a-h, large lower case, eighths ; a-p, 

 small lower case, sixteenths. The levels of corresponding pieces of P. doro- 

 tocephala are in part slightly different from those indicated in the diagram 

 since in this species the posterior zooid is much longer and the pharynx 

 therefore nearer the anterior end in large animals than in P. lata. 



