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Scientific Proceedings (130) 



It is to be noted that large larvae were present in the bottle when 

 it was placed in the cold. These were presumably six days old 

 and within twenty-four to forty-eight hours of pupation. When 

 the bottle was removed from the cold a few pupae were present. 

 Presumably these were the first to hatch and are included in the 

 first count; and since all of the flies in this count are modified it 

 may be inferred that these had not passed the critical stage when 

 placed in the cold. This would place the critical stage near the 

 end of the larval period or in the early pupal period. Experi- 

 ments now under way ought to locate the time accurately. An- 

 other noticeable feature in the above experiment is that in the 

 first count all of the eighteen flies are delta-like, whereas in the 

 next count only two out of the thirteen modified flies show this 

 characteristic. This suggests that the effect on the fifth vein is 

 produced relatively later in ontogeny than that on the bristles, 

 particularly the scutellar bristles. 



Another bottle carried along with the one just considered, but 

 left in the cold a shorter time gave very similar results. A third 

 treated at a different time and left longer in the cold did like- 

 wise, except that only five delta-like flies appeared and these were 

 in the second count instead of the first, although the other modi- 

 fications appeared in the first. 



It has been shown by Krafka 3 that in the bar-eye race of D. 

 melanog aster temperature exerts an influence on the extent of 

 reduction of the eye, and that it acts before pupation, during 

 the third to fourth day of development (when the embryo is 

 from 32%-45% developed). Likewise Hoge 4 has shown that 

 temperature affects the manifestation of "reduplicated legs" in 

 the same species. Here it is effective on the egg instead of the 

 larva. The present results more nearly resemble those of Krafka, 

 although the critical period may not come at exactly the same 

 stage in the two cases. They also appear to agree in that the 

 effect is produced before the organs concerned are laid down in 

 the pupa. 



The similarity of response to cold on the part of the bent race 

 in D. melanogastcr was shown by experiments similar to those 

 outlined above. In one of these a lot of bent flies from stock 5 



3 J. Gen. Physiol, 1920, v, 433. 



4 J. Exp. Zool, 1915, xviii, 241. 



5 I am indebted to Professor T. H. Morgan for this stock. 



