Cases of mimic mutations and secondary mutations in the X-chromosome &c. 



The sterility of the singed females. 



In order to obtain a pure singed stock, singed females were bred 

 to singed males, but no offspring were produced. Singed females were 

 then tested in mass cultures and on a large scale, by males from the 

 wild and from several mutant stocks. They were seen to copulate 

 with the males in the usual way, and after some days their ovaries 

 contained a seemingly normal 

 number of eggs at different 

 stages of development. But they 

 proved to be entirely sterile not 

 only with their own but with all 

 males. 



To determine the nature of 

 this sex-limited sterility virgin 

 singed females were mated (2294, 

 Nov. 7, 1920) and isolated in se- 

 parate glass tubes with banana 

 agar culture media. An equal 

 number of their heterozygous 

 sisters of same age and kept under 

 equal conditions served as control 

 (2295). The following day the 

 three singed females had laid 

 10, 2 and 5 eggs respectively 

 while their heterozygous sisters 

 had laid 5, 6 and 6 eggs. 



However, the eggs of the 

 singed females looked very diffe- 

 rent from the normal eggs of 

 their heterozygous sisters. They 



were very much shorter, and seemed to lack the two filaments nor- 

 mally present. 



The. ovaries of singed females were now dissected, and it was 

 found that the eggs in realty possessed two filaments but these were 

 shorter, broader, and more flattened towards the end than those of 

 normal eggs. Their insertion was shifted to a place a little anterior 

 to the middle of the egg while those of normal eggs have their position 

 near the anterior end (Fig. 2). 



Fig. 1. Singed male. 



