270 



RALPH S, LILLIE. 



At 31° the conditions become more favorable and with the 

 proper times of exposure practically all mature eggs form fertiliza- 

 tion-membranes, and in favorable cases the great majority 

 develop to larvae. Four series of experiments were performed 

 at this temperature; in one of these (August 28) only about half 

 the eggs underwent maturation, and with 15 minutes' exposure 

 (approximately the optimum) only 10 to 15 per cent, of all eggs 

 formed larvae. In the other three series the eggs were normal. 

 The proportions of eggs forming membranes and larvae in these 

 series with the different times of exposure are given in Table III. 



Table III. 



31"- 



At this temperature an exposure of 3 to 4 minutes is required 

 to cause membrane-formation in 10 per cent, or more of the eggs; 

 exposure must be prolonged to ca. 8 minutes before any eggs 

 form larvae; 14 to 15 minutes is the approximate optimum. In 

 the series of June 12 this optimum was not reached. 



At 32° a larger number of experiments were performed than 

 at any other temperature, and their results show a decidedly 

 greater uniformity than at lower temperatures. With the 

 optimal times of exposure (from 7 to 8 minutes) the proportion 

 of larvae yielded by normal eggs is always high, — usually over 

 90 per cent. This is illustrate(jl by Table IV., which summarizes 

 the results of six successive series performed during June at a 



