180 



THE SECOND-CHROMOSOME GROUP 



gial ("repulsion"). FI males from these matings were back-crossed 

 singly to purple vestigial females from the stock. The parents were 

 in several cases transferred at the end of 10 days to fresh culture- 

 bottles and second broods then raised. 



TABLE 3 1. 1 B C. offspring given by the FI mid-type sons, from the outr-cross 

 of a purple vestigial male to a wild female, when back-crossed to purple 

 vestigial females. 



'This table and table 32 were included by Morgan in his paper on "No crossing-over in the 

 male of Drosophila ..." Biol. Bull., April, 1914, pp. 200 and 201. 



The offspring from the " coupling" experiment (5 pairs, both broods, 

 table 31) gave a total of 1,071 flies, not one of which was a cross-over, 

 and the "repulsion" experiment (3 pairs, both broods, table 32) added 

 704 more (total, 1,775), not one of which was a cross-over. Since 

 these were back-cross experiments, there was no masking of results 

 possible, and cross-over gametes had every opportunity to reveal 



TABLE 32. B. C. offspring given by FI wild-type sons, from out-cross of purple 

 male to vestigial female, when back-crossed to purple vestigial females. 



themselves had any been formed, so that each fly recorded above is a 

 true non-cross-over. While the total absence of cross-overs in these 

 repetitions of the male test did not prove that the apparent cross-overs 

 in the original test were not genuine, it added to the already large 

 body of evidence which showed that they were at least aberrations 

 from the normal condition. 



