300 



POPULATIONS 



has a wide ratio of total life span to mean 

 duration of life. In the males this ratio is 

 about 304:100, and in the females 219: 

 100. For the human life table the corre- 



In the chapter on Biological Backgrounds 

 certain illustrations were presented that 

 made use of life table data, particularly in 

 terms of survivorship. Figure 73 (p. 274) 



-100 -50 50 100 150 200 



PERCENTAGE DFVIATION FROM MEAN DURATION OF LIFE 

 Fig. 93. Fearl's three categories of survivorship curves: Group A, "rectangular type;" Group 

 B, "intermediate type;" and Group C, "diagonal type." ( From Pearl. ) 



sponding ratios are 179:100 and 169:100." 

 In addition to this general similarity the 

 Tribolium curves have at the beginning of 

 life in the imago stage a component corre- 

 sponding in time and quantitative relations 

 of its incidence to the infant mortahty com- 

 ponent of human life tables." 



shows the /^ curves for Drosophila reared 

 under laboratory conditions. If we re- 

 examine this graph from our present point 

 of view and pay particular attention to 

 curve "3," wild type flies and curve "4," 

 vestigial type flies, we can add a bit of in- 

 formation to this discussion of the Ufe table. 



