35(3 



bulletin: museum of comparative zoology. 



(Partial resorption followed regeneration) was measured and likewise 

 the area between the two curves. The latter was expressed as a 

 per cent of the former. The result is a quantitative expression of 

 retardation (or acceleration) of regeneration which can be compared 

 wuth similar quantities for other experiments, whereby are avoided 

 such errors as would arise from differences between the degree of 

 regeneration of the control in different experiments. 



Acceleration and retardation were found to result from different 

 types of exposure, as seen in Figs. 5 and 6. The conditions determin- 

 ing whether acceleration or retardation will occur are shown by the 

 correlation tables (Figs. 7 and 8), which include the results of all 

 experiments. The ordinates indicate the number of hours of exposure 



Fig. 7 — Correlation table sho\ying the relation between length of exposure and 

 per cent of retardation. 



The units of the ordinate indicate the hours of exposure. 



The units of the abscissa indicate per cent of development. 



The numbers in parentheses indicate relative development before beginning of 

 exposiu'c. 



to radium. The abscissas in Fig. 7 stand for per cent retardation, 

 and in the next table, for per cent acceleration calculated from the 

 areas of the curves. The dots in Fig. 7 and tlie circles of Fig. 8 stand 

 each for an experiment. The connecting of a dot to a circle is to show 

 that acceleration and retardation occurred at different times in the 

 same experiment. 



The chief cause of the acceleration shown in Fig. 8 is apparent 

 upon comparing the lengths of treatment in it with those which pro- 



