8o 



SENESCENCE AND REJUVENESCENCE 



vertical column gives in hours and minutes the length of time in 

 cyanide at each examination; the second gives the serial number 

 of each lot, and the five columns headed by Roman numerals under 

 ''Stages" give the number of animals of each lot in each stage of 

 disintegration at each examination. In this case Lot i consists 

 of ten young worms, four to five millimeters in length, and Lot 2 



Stages and 

 their values 



Hours o ^ 



Fig. 3. — Planar ia dorotocephala: susceptibility curves of young (06) and old 

 (cd) animals in KCN o.ooi mol. Graphic presentation of the data of Table I. The 

 vertical inter\'als represent the arbitrary numerical values of the average disintegra- 

 tion stages, the horizontal intervals half-hour periods. 



of ten old worms fifteen to sixteen millimeters in length, both from 

 the same stock. 



The table shows that in the young worms of Lot i disintegration 

 begins earlier and proceeds more rapidly than in the old worms of 

 Lot 2. The young worms have all reached Stage V after two and 

 one-half hours in cyanide, while none of the old worms have reached 

 this stage at this time and all of them reach it only after five and 



