No. 584] REGENERATION IN ENCHYTRJEVS 499 



tween the two observations, so that the total number of 

 observations recorded in any one set of experiments may 

 be larger than the number of worms observed in the 

 same set. 



The results of these experiments are summarized in the 

 graph shown in Fig. 1, where the rates of regeneration 

 per day (expressed in hundredths of the length of one 

 segment) are measured on the axis of ordinates (Y), 

 and the length ( in number of segment- ) of the piece- that 

 produced the regenerated parts, are measured on the axis 

 of abscissae (X). Since sixty is about the average num- 

 ber of segments in this species, that is the value which 

 has been used in plotting the curve. A mathematical 

 analysis of the rates of regeneration at the different levels 

 shows that the difference in the mean rates of regenera- 

 tion at any two successive levels is significant. But the 

 temperature of the worms was not carefully controlled, 

 and the periods during which the wounds were healing 

 and the worms preparing to form new segments were in- 

 cluded in the computation of the mean rates of regenera- 

 tion. Therefore, the ratio between the rates of regenera- 

 tion, as here computed, at any two of the six levels only 

 approximates the ratio which would have been obtained 

 between the rates at these two levels by subjecting all the 

 worms to the same temperature conditions and by using 

 in the computation of the mean rates of regeneration only 

 the periods during which the segments were being formed. 

 The curve suggests, however, that the rate of regenera- 

 tion for the posterior half of the body is proportional or 

 nearly so, to the number of segments removed. Anterior 

 to the twentieth segment the rate of regeneration de- 

 creases. May we not have here a curve depending on two 

 opposing sets of factors; one which tends to increase the 

 rate of regeneration as more segments are removed, the 

 other to decrease the rate? In the latter set of factors 

 the amount of available building material may be the most 

 important element. 



