DYNAMICS OF MORPHOGENESIS 177 



within six and one-half hours, Lot 2 within twenty-eight and 

 one-half hours. In other words, Lot 2 requires a little more than 

 four times as long as Lot 1 to reach a given stage of disintegra- 

 tion. As in the cases of the two alcohol series the differences in 

 physiological resistance in the two lots are of the same order of 

 magnitude as the temperature coefficient of chemical reaction for 

 15°. Moreover, they are certainly far greater than any possible 

 differences in the coefficient of distribution for the temperature 

 interval used. 



And finally, the most interesting fact of all is that when the 

 differences in resistance as expressed in the times required to 

 reach a certain stage in the three series, 561, 562, and 521 are 

 reduced to the same terms, e.g., to a temperature interval of 

 10°, they are practically identical. This fact is seen in table 6. 

 The table shows the relation between the times required to reach 

 given stages in the two lots of each series. For Lot 1 in each case 

 the time is taken as unity. 



The table shows that, at least for the stages considered, the 

 rapidity of disintegration increases about three times for a rise 

 in temperature of about 10°C. The close correspondence of the 

 figures is all the more striking when it is remembered that in 

 Series 561 large old worms were used, the temperature interval 

 was 10° and alcohol 5 per cent was the reagent, while in Series 562 

 small young worms were used, the temperature interval was 5° 

 and alcohol 6 per cent was the reagent, and finally, in Series 521 

 II large old worms were used, the temperature interval was 15° 

 and KCN 0.001 m. was the reagent. This constancy of results 

 indicates that the essential factor is in all these cases the same. 

 The temperature coefficient of physiological resistance of Planaria 

 dorotocephala to alcohol and KCN is then about 0.33 for a rise 



one-half hours, but Lot 2 does not reach a stage corresponding to the first recorded 

 stage of Lot 1, with six worms intact and four beginning to disintegrate until ten 

 and one-half hours. Evidently then, the full difference between the two lots is 

 given only by comparison of these corresponding stages. This gives us a relation 

 of 1 : 4.2 while if we take the first recorded times of disintegration for both lots 

 we obtain a relation of 1 : 3. The discrepancy between these figures is due simply 

 to the fact that the time of the earliest stages of disintegration in Lot 1 was not 

 recorded. There can be no doubt that the proportion 1 : 4.2 is more nearly 

 correct than the other, 1:3. 



