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RAPLH S. LILLIE. 



twenty or twenty-five times as rapidly at 35° as at 30°. Thus 

 at 30° the minimum exposure for membrane-formation is about 

 10 minutes, and at 35° 30 seconds or less; similarly at 30° the 

 minimum exposure needed to induce even a few eggs to form 

 larvae is about 20 minutes, at 35° it is about i minute ; at 30° the 

 optimum exposure is ca. 30 minutes, and at 35° ca. i}^ minutes. 

 For each temperature it is possible to assign a definite length of 

 exposure which produces a definite effect on the egg. The 

 manner in which these times of exposure vary at different 

 temperatures may be seen by reference to Table IX. Here are 



tabulated the observations made in all of those series of experi- 

 ments in which a large proportion of eggs formed larvae, — in 

 which, therefore, the conditions may be regarded as essentially 

 normal. In the series at 29° few eggs formed larvae; at 30° only 

 one series out of five gave a considerable proportion of larvae {ca. 

 40 per cent.) with ca. 30 minutes' exposure; in all of the other 

 series in the table, except one at 31°, the great majority of eggs — 

 usually over 90 per cent. — formed larvae with the optimal 

 exposures. In the first column is given the least time of ex- 

 posure required for membrane-formation in a significant pro- 



