170 HAROLD H. PLOUGH 



first ten day period, after mating. The value is nearly fifteen 

 units higher than the first brood control No. 5, and more than 

 eighteen units higher than the corresponding second brood taken 

 after ten days at 22°, No. 6. Such a striking difference proves 

 conclusively that the percentage of crossingover can be increased 

 in the second brood by simply keeping the parents at the high 

 temperature while they are laying the first, even though that 

 first brood shows no increase whatsoever. This point is more 

 firmly established by No. 9 and No. 10. No. 9 is the first brood 

 taken from females hatched at 31.5° but mated and kept for the 

 first ten days at 31.5°. The usual increase over No. 5 was shown. 

 The second brood, No. 10, was laid at 22°, yet it remains at the 

 high point, instead of dropping as did No. 4, when the first brood 

 of a similar mating was taken at 22°. Taken as a whole, the 

 data in table 11 clearly establish the fact that high temperature 

 is effective in increasing the percentage of crossingover only for 

 the brood taken immediately after the exposure for ten days, 

 and that this exposure may occur either while the female is 

 going through its metamorphosis or after it has reached the adult 

 stage and has been mated. 



Fractionations of brood counts 



The value for the black-purple region given in No. 9, table 11, 

 is 15.8, while the value for the same region at approximately 

 the same temperature given in table 8 is 14. The only difference 

 is that the table 9 value was given in a culture kept at 31.5° 

 rather than at 22°. This increase suggests the possibility that 

 some effect of the temperature at which the brood is laid may be 

 registered even within the ten day period of the brood in question. 

 It may mean that the early part of a count would give a higher 

 crossingover value than the later part in the first brood of a 

 female which had been exposed to heat up to the time of hatching 

 but mated at 22°. In other words, only part of the eggs in any 

 brood may be affected by the temperature during the previous 

 ten day period, and part of them by the temperature to which 

 the female is exposed while laying that brood. Since any bottle 

 is usually counted at about two day intervals, it is possible by 



