380 



GENES MODIFYING NOTCH. 



with injured eyes that have developed into smaller eyes, i. e., dwarf 

 whole eyes. Three conditions make this interpretation improbable. 

 In the first place, the reduced eyes are often identically the same on 

 the two sides, which would 

 scarcely be expected if due 

 to accidental puncture by a 

 larva. In the second place, 

 several individuals with re- 

 duced eyes often appear 

 at the same time, while for 

 long periods none at all are 

 present. Some unknown 

 environmental factor would 

 seem the most probable ex- 

 planation, especially when 

 the offspring of Notch in- 

 dividuals do not repeat the 

 eye condition. Probably 

 some lethal combination 

 may be involved. In the 

 third place, the individuals 

 which are not Notch have 

 never shown this modification of the eyes. At the time when the de- 

 formed eye was most frequent (winter of 1917) records were kept of 

 its frequency in mass-cultures (usually F2 parents and F2 offspring). 



Fig. 100. 



In the culture F5 there were 13 Notch with deformed eyes. These 

 were all bred together with their normal brothers and sisters with 

 eosin eyes and gave : 



Fe: Notch 9 , 56; deformed 9,4; eosin 9 , 65; eosin cJ', 48. 



The offspring of this line, part of which are included in the F7 count 

 in the preceding table, gave occasionally deformed-eyed flies, but not 

 more frequently than sister cultures. 



