CF.OSSINGOVER IN DROSOPHILA 



169 



TABLE 11 



S' 



NUM- 

 BER 



DESCRIPTION 



Control bred at 22° 



Second brood after 10 



days at 22° 



Heat 31.5°, bred at 22°.. . 

 Second brood after 10 



days at 22° 



per cent 

 20.5 



14.9 

 29.8 



17.8 



bl pr cv 



9 

 10 



Control 22°, bred at 22°.. 

 Second brood after 10 



days at 22° 



Third brood after 20 days 



at 22° 



Second brood after 10 



days at 31.5° 



Heat 31.5°, bred at 31.5°.. 

 Second brood after 10 



days at 31.5° 



19.5 



17.9 



18.0 



32.6 

 31.3 



18.6 



of the heat. The second brood from these parents, No. 4, after 

 ten days at 22°, gave a value very close to the control second 

 broods (No. 2) and twelve units less than the first brood value 

 (No. 3). Such a decided falling off can mean only one thing, 

 namely, that the second brood values for females which had been 

 treated with high temperatures up to the time of hatching, closely 

 approximate the corresponding values for flies not so treated, 

 and that the heat effect is no longer observable after the first 

 ten day period. For Nos. 5 to 10, a different stock was used, 

 black-purple-curved, and both crossingover percentages are 

 significant, though the shorter one— black to purple, per cent I — 

 is the more reliable. No. 6 shows the usual second brood de- 

 crease below No. 5, while No. 7 confirms the observation of 

 Bridges that third broods show a tendency to return to the 

 value for the first brood. No. 8, however, gives the values for 

 second broods when the females were kept at 31.5° during the 



