Illustrations 



35 Survivorship, death and death-rate curves for the black 

 widow. 131 



36 Survivorship curves for male and female Tribolium madens 131 



37 Effect of restricted food upon the longevity of Daphnia 

 longispina 144 



38 Effect of restricted food upon the duration of instars in 

 Daphnia longispina 145 



39 Effect of restricted food upon the rate of senile change in 



the heart rate of Daphnia longispina 146 



40 Survival curves of normal and retarded male and female 

 rats, showing the effect of dietary restriction 149 



41 Neutral 1 7-Ketosteroids, 24-hour urinary excretion of 

 human males 1 73 



42 The postnatal growth in weight of male children 1 84 



43 Annual growth increment in boys, from the data of 

 Quetelet 184 



