144 SUMMARY OF CURRENT RESEARl I IKS RELATING TO 



There is evidence that a larger percentage of the F! generation have 

 beaded wings when the culture is wet and the food alkaline There is 

 also evidence of a gene which hehavesasa lethal factor preventing the 

 development of any fly that carries it in a homozygous condition. 

 Whether the gene concerned in the production of beaded wings is 

 dominant or recessive is determined probably by (1) the nature of the 

 egg cytoplasm ; (2) the presence or absence of the lethal gene ; and 

 (3) the nature of the environmental conditions. 



Failure of Ether and Radium to produce Mutations in Droso- 

 phila.* — T. H. Morgan has enquired into the possibility that ether or 

 radium may have brought about the mutations which he has observed 

 in Drosophila ampelophUa. In a total of 31,168 flies subjected to ether, 

 there was not a single mutation observed, so that it seems safe to say 

 that ether does not play the role of a specific agent causing the muta- 

 tions. Experiments on a large scale in subjecting the flies to the 

 emanations of an X-ray machine and of radium salts failed to produce 

 any mutations, although the flies were made sterile for a time. At 

 various times experiments have also been made with changes of tem- 

 perature, salts, sugars, acids, and alkalis, without any resulting mutation. 

 Guyenot also treated the fly to high temperatures, to radium, and to 

 X-rays without result. Many mutants of Drosophila are known, but 

 their occurrence seems to be very rare. They appear under conditions 

 where all the other flies in the same culture are normal. But it is not 

 known whether they are evoked by external influences, accidents of 

 mitosis, hybridizing, changes in the chromosomes, or otherwise. 



Apterous Drosophila.f — Charles W. Metz has studied the heredity 

 of an apterous mutant of the fruit fly, Drosophila ampelophUa. The 

 apterous character is a simple Mendelian recessive, which independently 

 mendelizes with miniature wings, white eyes and vermilion eyes, and 

 hence is not sex-linked. The apterous factor is transmitted independently 

 of the factor for pink eye. It is distinct from vestigial wing. It is 

 closely linked to black. 



The apterous mutant is not only entirely destitute of wings but has 

 greatly reduced balancers. It is weak, sluggish, short-lived, and with a 

 marked incapacity for reproduction. Germ-cells are produced normally, 

 but the individuals evidently find it difficult to perform the reproductive 

 processes. 



No crosses were obtained between apterous and apterous, but each 

 sex was successfully crossed with winged forms. The apterous female 

 could produce only a few eggs. 



Although many opportunities were given, no apterous form gave 

 rise to a vigorous race. It seems that vigour and viability are directly 

 associated with morphological characters, and are not to be separated 

 from them by selection. In other words, the factor responsible for lack 

 of wings is also responsible for physiological disturbances. The case 

 shows that a factor may have far-reaching effects, and need not be 



* Amer. Naturalist, xliii. (1914) pp. 705-11. 



t Amer. Naturalist, xliii. (1914) pp. 675-92 (1 fig.). 



