78 Chromosomes and Linkage Groups. 



exceed the haploid number of autosomes. In loillistoni, which has 

 only two pairs of autosomes (unless the m-chromosomes are present 

 but are so small as to have escaped detection), only two groups of 

 non-sex-linked characters have been found. One of these contains 

 eight characters and gives a long map; the other contains six char- 

 acters, but their linkage relations are not yet worked out. 



In ohscura where four pairs of autosomes are represented, two 

 autosomal linkage groups with four or more characters each, are 

 known; and preliminary results indicate that the other two are prob- 

 ably represented by one character each (unpublished data of D. E. 

 Lancefield). 



In D. melanog aster, as is well known, the four linkage groups show 

 a fairly close correspondence to the four pairs of chromosomes, both 

 as regards number of loci and amount of crossing-over. In the 

 other species (at least simulans, virilis, and willistoni) the evidence 

 points in the same direction. 



D. H. HILL LIBRARY 



