Effects of Temperature on Drosophila 307 



the modifications revealed only by the cold in bent virilis are like- 

 wise revealed here. These will be noted more specifically below. 



Another feature brought out by these experiments is that ex- 

 posure to cold produces its effect at a fairly definite time in 

 ontogeny. Space forbids going into the details of the experi- 

 ments, but a few data may be cited. In one experiment a stock 

 bottle (bent virilis) was put directly into the cold when made 

 up and left there for forty seven days at a temperature varying 

 from about 9° to 12° C. This is more than three times the ordi- 

 nary developmental period in the incubator (23° C), but the 

 embryos were still in the larval stage when removed from the 

 cold. None of the flies from this bottle showed any noticeable 

 effect of the cold, which suggests that they were not treated at a 

 late enough stage. Another similar experiment gave the same 

 result. 



In another experiment a bottle of bent virilis was kept in the 

 incubator as usual for six days, then transferred to the cold for 

 eighteen days, then kept constantly in the incubator. The eyes 

 showed considerable effect in the early counts and then became 

 more like those of ordinary bent in the later ones. In addition 

 other modifications were observed as follows : ( 1 ) one or more 

 scutellar bristles misplaced or absent (abbreviation sc) ; (2) one 

 or more sternopleural bristles absent (stp) ; (3) apex of fifth 

 vein thickened delta-like (del). Table 1 includes a record of 

 the flies hatching from this bottle, together with the number 

 of days elapsing between the time the bottle was removed from 

 the cold and the time the flies were taken from the bottle. The 

 eye modification, being difficult to classify accurately, is omitted 

 from the table. 



TABLE I. 



Stock bottle "bent (virilis). Incubator 6 days; cold (approx 9-ll°C.) 

 18 days; incubator remaining time. Pupae present when removed from 

 cold. The first column indicates the number of days after the bottle was 

 removed from the cold. 



Days 









del. 











after 





del. 



del. 



sc. 





sc. 







cold 



del. 



sc. 



stp. 



stp. 



sc. 



stp. 



stp. 



none 



( 7) 



8 



4 



4 



2 



0 



0 



0 



0 



(10) 



0 



2 



0 



0 



11 



0 



0 



44 



(16) 



0 



0 



0 



0 



0 



0 



0 



57 



(17) 



0 



0 



0 



0 



0 



0 



0 



10 



(23) 



0 



0 



0 



0 



0 



0 



0 



40 



