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THE AMERICAN NATURALIST [Vol. XL VIII 



dominant. The conditions so far presented which cause 

 it to be dominant are two. (1) The presence of a gene 1 

 in the second chromosome which can not exist in the 

 homozygous condition. (2) The influence, particularly 

 noticeable in the males, of non-chromosomal constituents 

 of the egg from which the individual arose, so that if the 

 mother had been Beaded, the appearance of Beaded wings 

 in her sons would be increased, and if the mother had been 

 normal the appearance of Beaded wings in her sons would 

 be reduced. 



Certain facts already brought out (namely, those pre- 

 sented in Tables II and III) show that the tale is not yet 

 told. Our hypothesis does not explain the fact that from 

 definite numbers of eggs laid at different periods in the 

 life of an individual very different percentages of Beaded- 

 winged offspring arise, and these differences do not form 

 a definite series progressing to or from a high percentage 

 as the individual grows older, but are extremely irregular. 

 We have not gained control over this phenomenon, but 

 the evidence we have to present points strongly to the 

 suggestion that the environmental conditions are the final 

 determiners of the percentage of the Beaded-winged off- 

 spring. This environmental control might lie in three 

 distinct methods: (1) The destruction of a certain class of 

 offspring by their differential viability. (2) In the case 

 of Table III the results might be explained on the theory 

 that Beaded flies had a shorter life cycle. This supposi- 

 tion has, however, been disproved as follows. Five non- 

 virgin females from Beaded-winged stock and five non- 

 virgin females from normal-winged stock were put to- 

 gether without males in the same bottle. When the off- 

 spring began to hatch they were examined daily. During 

 the first three days 73 flies hatched, of which 11, or 15 per 

 cent., had Beaded wings. During the following five days 

 261 flies hatched, of which 54, or 20 per cent., had Beaded 

 wings. Since I was particular to take Beaded flies several 

 days old as the parents of these Beaded offspring, the 

 experiment shows that if there is any difference in the 

 length of the larval life, that of normal-winged flies is 



