THE RECONSTITUTION OF ISOLATED PIECES 



117 



dashes), and ten animals developed from the 6-pieces (ab, unbroken 

 line). The figure shows that the susceptibility of animals resulting 

 from the reconstitution of pieces is practically the same as that of 

 the young, growing, sexually produced animals of the same size 

 and much greater than that of the old, sexually mature animals. 

 In other words, the animals resulting from experimental repro- 

 duction possess about the 

 same rate of metabolism as Stages 

 sexually produced growing 

 animals of the same size, and 

 a much higher rate than the 

 animals from which the pieces 

 were taken. The process of 

 reconstitution has made the 

 experimentally produced ani- 

 mals as young as the sexually 

 produced animals of the same 

 size. 



It is of interest, however, 

 to note that the ^-pieces from 

 the posterior end of the ani- 

 mal (Fig. 26) show a some- 

 what greater susceptibility 

 than the a-pieces from the 

 anterior body region. This 

 difference in susceptibiHty 

 corresponds to a real differ- 

 ence in the process of recon- 

 stitution in pieces from these 

 two regions. In the recon- 

 stitution of the 5-pieces there is less outgrowth of new tissue 

 and more reorganization of the old than in the a-pieces, so that 

 the old tissue becomes somewhat younger in the former than 

 in the latter; consequently, as the new tissue becomes older and 

 the old tissue younger, they finally attain the same physiological 

 age at a stage somewhat younger in the ^-pieces than in the a- 

 pieces. Shght differences of this kind are characteristic of pieces 



Hours 1234 



Fig. 27. — Susceptibility of Planaria macu- 

 lata to KCN o.ooi mol.: ab, long dashes, 

 sexually produced young; ab, short dashes 

 and unbroken line, animals resulting from 

 reconstitution of pieces; cd, animals like 

 those from which the pieces were taken. 



