94 



the most interesting and important features of their economy. Pre- 

 vious attempts to estimate the possible number of offspring descending, 

 under ideal conditions, from a single female San Jose scale during a 

 season, have not taken sufficient account of the many complex factors 

 of the problem. The writer has here attempted to make such an esti- 

 mate w^ith some degree of accuracy, having in view the percentage 

 of males, the periods of growth, and the rate of reproduction in each 

 generation. The data relative to the percentage of females are from 

 Mr. Pergande's Washington experiment of 1,896, and the others are 

 from Mr. West's experiment. They are summarized in the following 

 table. 



From these data were obtained the number of young that would 

 be produced for periods of 142 days, 152 days, and 162 days, respec- 

 tively, as shown in the following table. 



The figures in the middle column are for the season of Mr. West's 

 experiment, which began May 30, and closed October 28. Taking the 

 growth period of the males as twenty-five days, and their adult period 



^Assumed , 



